+ All Categories
Home > Documents > Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf ·...

Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf ·...

Date post: 10-Dec-2018
Category:
Upload: vohanh
View: 220 times
Download: 0 times
Share this document with a friend
12
The Water and Sanitation Program is an international partnership for improving water and sanitation sector policies, practices, and capacities to serve poor people August 2004 Field Note The Case for Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta – has been largely achieved through the private sector supplying individual households. Evidence from what works indicates that development of the market is the only sustainable approach to meeting the need for sanitation in the developing world. This field note explains the marketing approach and suggests that it should be promoted as a central feature of sanitation improvement programs.
Transcript
Page 1: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Water and Sanitation Programis an international partnership forimproving water and sanitation sectorpolicies, practices, and capacitiesto serve poor people

August 2004

Field Note

The Case forMarketing SanitationAccess to sanitation – the hygienic disposal of human excreta – has been largely achieved through theprivate sector supplying individual households. Evidence from what works indicates that development ofthe market is the only sustainable approach to meeting the need for sanitation in the developing world.This field note explains the marketing approach and suggests that it should be promoted as a centralfeature of sanitation improvement programs.

Page 2: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

������������ � ���

Sanitation – the hygienic disposal of humanexcreta – is a basic human need. However,2.4 billion people, or more than half thepopulation of the developing world, still lackit. To halve that fraction by 2015 is aMillennium Development Goal. Millions ofdollars in sanitation programs have madelittle impression, especially in Asia andAfrica, where the shortfall is greatest. Mostprogress in access has been achieved bythe market – private suppliers supplyingindividual households. The only sustainableapproach to meeting the need for sanitationin the developing world is to support thatmarket. Marketing has been moresuccessful than anything else in changingthe behavior of people when they can seedirect personal benefits. The purpose of thisfield note is to explain the marketing

approach, and suggest how it can be acentral feature of future national sanitationimprovement programs.

Benefits of sanitation

Improved health may seem to be the mostobvious benefit of sanitation (see Box), butother gains are no less important. Theseinclude:� Convenience and comfort� Privacy and safety� For women and girls, avoidance of

sexual harassment and assault� Less embarrassment with visitors� Dignity and social status

Because of these other benefits, a largenumber of people – even very poor people –are willing to pay for basic sanitation.

Public and privatedimensions

Sanitation involves products and servicesnot only at the household level, but alsofor the community as a whole. Theseyield private and public benefits. Theindividual household’s toilet is a privateaffair, and the household is usually willingto pay for its benefits. The othercomponents of the system, such as thesewerage network or a pit emptyingservice, and the final treatment anddisposal of the wastes, affect everyoneand need public management.

This field note does not discuss publictoilets. Though public toilets with anadmission charge can be very successfulas a business, they are not usually anadequate solution to households’ sanitationneeds. For example, they are usually

����������������������� ������������

������������������������������������

���������������������������������������

������������������������ ���������������������

����������������������������� ���������

�������������������������������������

���������������� !"# $%�

����������������������������&���������

�������������������������������������

����������������������'

�� !�������������&��������������

��������������������������������

�����������������������������'

(� ��������������������������������

���������������������������

��������������������������

��������'

)� %������������������&�������

����� �����������������������

���������� ��������������

�����

Health benefits of sanitationlocked at night and are not used fordisposal of young children’s stools.

If sanitation is so good,why don’t people buy it?

The short answer is that people do pay forsanitation – in their millions – whenconditions are favorable. For example, thefigure below shows the changes in overagewith different sanitation technologies inKampala, Uganda, from 1992 to 2003. Itshows how the extension of coverage,mainly with septic tanks and pit latrines, hasmore than kept pace with the city’s growingpopulation, which nearly doubled in just overa decade. Indeed, the proportion of thepopulation without their own sanitation (whohave access only to a shared latrine or tonone) fell from three quarters to less thanhalf, although there was no major public

Many people in the world live without proper sanitationthough they need it badly.Photo credit: Kameel Virjee

Tackling the millennium sanitation goal calls for fresh thinking and innovative approaches.Marketing sanitation, building on perceived benefits, offers a new approach to ensure thatcommunities have access to safer services.

Page 3: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Case forMarketing Sanitation

program to build or promote sanitationduring that period.

Nevertheless, many people in the worldcontinue without sanitation, though theymay say they want it badly. Why? Onereason is that sanitation is most important towomen and children, though it is men whomake the investment decisions in manycommunities, and they may have otherpriorities.

Another is the conflict of interest betweenlandlords and tenants. Landlords oftenconsider it unnecessary to spend moneyinstalling sanitation facilities in theirproperties, if they are not compelled to doso. Poor tenants, with little bargainingpower, may fear that if they invest insanitation themselves, their rent may beincreased or they may lose their tenancy,and hence their investment. Another reasonis the frequent lack of good home sanitationinformation, products and services at anyprice.

Engineers, administrators and by-laws havealso impeded sanitation when theyprescribe technologies, such aswaterborne sewerage systems, that are tooexpensive, not only for the poor but also forlocal governments.

The urgent need today is not for thesame technology which is found in theindustrialized world. For those whocurrently have nothing, a simple pit latrineor pour-flush toilet can be a majorimprovement in public health and farmore likely to be affordable.

Other constraints to demand have arisenfrom imperfections in the market for basicsanitation. People’s demand may bedampened by their previous unpleasantexperiences with deficient sanitation – forinstance when at school. They mayunderestimate the benefits andoverestimate the cost of sanitation, orlack confidence that local tradesmen canprovide a product of acceptable quality and

safety. For example, rumors of childrenfalling into pit latrines are a powerfuldeterrent to installing one at home. Serviceproviders also have often failed to offerpeople real choices with true costs thatcould meet their different needs. Instead,they have catered mainly for the relativelywealthy with toilet fittings designed forConventional, waterborne sewerage.

What is social marketing?

Marketing consists of activities by whichyou reach customers and persuade themto buy and use a product or service.Marketing works on the principle of avoluntary ‘exchange’ between consumerand producer where both gain. Consumersget benefits they want and producers gain

A simple pit latrine can be a major improvement in publichealth.Photo credit: Lukman Y. Salifu

Page 4: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

Product:��������������������������*������ ��������������������� ����������+ ��

��&����*# $%����� �����������+��������������*&���������������� �����������������+�

,������������������������������������������'�������������������������������

���������������������&�������������

Price:�,���������������������&�������������������������������������������

�����-������������������������������������� ���������������&�����������������.��/

���&�������

Place:�����������������������&����������������������� �������������������������

��&�������������������������&������� �������������&���������������� ����������

�����������������������

Promotion:�,������������������������������������������&��������������������������

����������������������������������������������������������

What is different about social marketing?

profits. Social marketing uses marketingtechniques to serve social objectives (seebox). Marketing goes far beyond mereadvertising. It is often said to have fourcomponents, the four Ps; product, price,place and promotion.

What does marketingmean for sanitation?

Product. Latrine designs must respond towhat people want, rather than whatsanitary engineers believe they shouldhave. In Mozambique, for example, themarketing of a new approach to sanitationbegan with many visits to existing latrinesand consultations with their owners. This‘market research’ revealed that mostpeople were used to open-air defecationand did not want a superstructure, beyonda matting fence for privacy. Their greatestneed was for a safe and affordable way ofcovering the pit. These findings led thegovernment to develop a round concretefloor slab, which could be manufacturedusing simple equipment in local workshops.

Usually, a range of different products areneeded to suit a variety of pockets andcircumstances.The Mozambican programoffered two sizes of slab, together withbricks to line the pit if necessary, and alatrine installation service.

Price. This is the hardest part of sellingsanitation to those who lack it. The poor,who need it most, can least afford it.Hence the need to keep costs down andmarket a range of products with variousprice tags. For example, in onesuccessful program in Bangladesh thecost of the latrines varied hugely, from aningenious design using tin sheeting forthe pour-flush pan and a flexible plastictube for an odor-proof seal, which costsonly Tk 15 (US$ 0.30), to a cement versioncosting US$500. For comparison, latrineprojects elsewhere in Bangladesh typicallyoffer a single model at a subsidized price;this limits the number of latrines that can bebuilt to the size of the subsidy budget.

Place. The product must be delivered to theright place; in particular, a latrine must beinstalled in the customer’s own home. Thismeans that the supply chain has to reachevery household. Sanitation programs inLesotho, Benin and elsewhere have trained

Promoting sanitation involves communicating with consumers about products and services.Photo credit: Andreas Knapp

Page 5: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Case forMarketing Sanitation

local masons not only to build latrines, butalso to do their own marketing.

In Mozambique, monitoring of the sales ofthe floor slabs showed that most purchaserslived within a few 100 meters of the pilotworkshop, and so a handcart was providedwhich customers could borrow to bring theirslabs home. The pilot workshop was thenused to train artisans for other localworkshops, each of which served its ownneighborhood. In Malawi and India,‘Sanitation marts’ have been set up as local‘one-stop shops’ selling a variety ofsanitation products and services.

Promotion. Promotion is communicationwith consumers about the product orservice. This includes advertising, massmedia, word of mouth, and anything inbetween. It can also include many othermeans to get customers’ attention andconvince them to buy the product:demonstration latrines, time-limited specialoffers, coupons and vouchers, competitionsand prizes, door-to-door sales, creditsponsored by local traders, and mutual helpschemes to help the poorest with the costand the elderly with the digging.

Promotion using mass media is mosteffective when it is well researched,professionally designed, and followed up byother communication opportunities whereconsumers can learn more.

So why marketsanitation?

First, marketing ensures that peoplechoose to receive what they want and arewilling to pay for. The last few decadeshave seen hundreds of thousands oftoilets built in the developing world, often

with considerable subsidy, by governmentand non-governmental organizations. Theimpact of such programs has usuallybeen very limited, because most of thetoilets were not properly used ormaintained. In other cases, very effectiveprograms for small numbers of familieshave in some sense ‘failed’ because thenumber built was tiny, compared with theneed.

A conventional subsidy-driven approachin Maharashtra State, India is considereda failure, despite its ‘success’ in building1.5 million toilets. Subsequent surveysreveal that more than half of these havebeen abandoned or are being misused.

Improved sanitation can assign dignity and boost socialstatus.Photo credit: Andreas Knapp

Page 6: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

Second, marketing is financiallysustainable. Programs which providesanitation at subsidized prices areconstrained by the size of the subsidybudget, which usually falls far short of theneed. Moreover, the subsidy is oftencaptured by the better-off, who are betterable to apply for it and spend it.

On the other hand, the private sectorcan make profits by selling sanitationproducts and services which consumersvalue and will pay for. Public fundscan then be used more effectively forproduct development, market research,training, promotion and other forms offacilitation.

Third, marketing is cost-effective and canbe taken to scale. Few conventionalsanitation programs have built more than10,000 latrines; and yet that is theminimum requirement for almost any majorcity in the developing world. This statisticshows that, with an average household sizeof six people, Kampala alone still needsten times that number.

Marketing, on the other hand, has beensuccessfully used by the private sector allover the world to sell all kinds of thingsfrom Coca-Cola to condoms. It’seffectiveness is easy to monitor bymeasuring sales.

Fourth, provision of hardware is notenough. Sanitation facilities will bring fewbenefits unless they are used correctly,and this requires changes in behavior.With a marketing approach, sanitationonly goes to those who purchase it,which makes it much more likely thatconsumers will understand its purposeand will value, use and maintain it.

Marketing has been succesfully used by the private sector to sell all kinds of products, including sanitation ware.Photo credit: Andreas Knapp

Subsidized sanitation programs are limited by the size of the budget and tend to benefit only a fewPhoto credit: Mvula Trust

Page 7: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Case forMarketing Sanitation

Role of the public sector

The marketing approach does not meanthat government should relieve itself ofthe responsibility for sanitation and leaveit to the local building trade. There is animportant role for government –especially local government – in thisapproach, but it is very different from thecommonly expected one of providingfacilities and services.

The public sector must:� Understand existing demand for

sanitation, and what limits it;� Overcome those limits, and promote

additional demand;� Stimulate development of the right

products to meet that demand;� Facilitate the development of

a thriving sanitation industry; and� Regulate and coordinate the

transport and final disposal ofwastes.

These five main activities are discussedbelow. There are several importantimplications of this shift. The publicsector must talk to:� Consumers� Manufacturers/builders/installers of

sanitation facilities� Providers of supporting services, e.g.

in emptying pits and septic tanks� Other public departments, such as

those responsible for urban landtenure, environmental pollution, smallbusiness development, etc.

Public resources for sanitation also needto be committed to:� Research and development� Promotion and advocacy� Training and capacity building

On the other hand public subsidies forlatrine construction should be avoided ifpossible. If not avoidable, they should bekept as low as possible, and preferablyused in ways that promote demand, andbe consistent with a subsidy policy that isaffordable at the scale needed to meetthe full sanitation challenge.

For example, subsidies could be used tooffer a low interest rate on loans for homeimprovement, or to exempt loans fromadministrative charges. Alternatively, asubsidy could be used for a limited-duration offer to attract attention to thelaunch of a new marketing campaign.Subsidies should never be applied in away which undermines the existingprivate providers in the market.

Building a latrine is a major investment formany poor households, so consumercredit may be important. However, itshould be used with caution, and kept toloans which can be repaid in less than ayear. When the poor are lucky enough toobtain larger loans, they will have otherpriorities. Many micro-credit lenders offerloans only for investments which generateincome, and that rules out sanitation.Lacking formal land tenure, the poor haveno collateral, though some lenders usepeer pressure or ‘social collateral’through self-help groups to ensure loanrepayments. A more promising use forcredit is to support small businesseswhich provide sanitation facilities andservices to the public, and wish toexpand.

The public sector has a vital role to play in coordinating final disposal of wastes.Photo credit: Andreas Knapp

Page 8: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The process ofmarketing sanitation

The marketing approach can besummarized in this sequence:

1. Win consensus

The first step is to establish a policyconsensus on the approach including a

policy on subsidies. This may be difficult

at the national level, where the traditional

approach of provision by government (or

none) has been followed for years. It may

Demonstrations can make it easier to market a product.Photo credit: Andreas Knapp

Page 9: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Case forMarketing Sanitation

be easier to gain the enthusiasm andsupport of relevant agencies in one city,or in one or two regions of the country.Successful demonstration of theapproach in one area will make it easierto extend to the country as a whole.

������������������� �������������� �

� ���������� ���� ����� �������

����������������� ���� ��

� �� ������� ����������� �������

�����������������������

2. Learn about the market

This means understanding both demand andsupply. On the demand side, find out whatpeople do at present to meet their sanitationneeds, who helps them to do it, at whatexpense, and why. Learning requires visits tomany existing latrines to observe their designand ask their owners why they are satisfied (ornot) with them.

Conversations with residents andlandlords of properties without sanitationwill also explain why they have ���invested in sanitation. Understandingsupply means talking with existing latrinebuilders, pit emptiers and other sanitationservice providers, which can yieldvaluable insights into their sales, costsand prices, and the constraints toincreased demand and increasedproduction.

Before the next step, check if thepreliminary findings suggest anymeasures to make the businessenvironment more favorable to the low-cost sanitation industry. For example,� Do building regulations rule out cheap

latrines?� Are the necessary building materials

readily available in suitably smallquantities?

� Does land tenure work to motivate orto deter intending purchasers?

Recent trends in coverage can beestablished by asking a representativesample of households with a latrine whenthey first acquired one. From their

Direct marketing is effective in building demand for sanitation products.Photo credit: Andreas Knapp

Page 10: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

responses, a retrospective ‘latrineacquisition curve’ can be drawn byplotting the percentage of householdswith a latrine (say) twenty years ago, tenyears ago and one year ago on a graphlike the example in the previous page.

The results of this enquiry can be used tohelp build consensus on the marketingapproach, as they will almost certainlyshow:

� How little progress in coverage hasbeen achieved by the conventionalapproach;

� That there is a dynamic market whichis already meeting the needs of manypoor people without any support fromgovernment;

� How a few simple measures taken bycentral or local government couldremove constraints and help todevelop the market further.

3. Overcome barriers,promote demand

Promoting demand for sanitation needsnew forms of partnership betweengovernment – especially local government– and the private sector providers ofsanitation services.

One step is to make existing regulationmore supportive. Restrictive buildingregulations can be replaced by manuals onhow to build various models of low-costlatrine.

Advertising is the best-known means ofbuilding demand. If mass media are used,an advertising campaign can be organizednationally, whereas production and salesare best organized locally. Where only a

limited proportion of the population isreached by mass media, additional channelsare needed, particularly word of mouththrough local field workers.

In addition to advertisements, the publicsector can help to overcome a lack ofcommunication and trust betweenconsumers and providers. It can buildmunicipal latrine show parks, where localhouseholders can come to view the differentmodels available, learn the true price of each,read testimonials from satisfied owners, andbe put in contact with reputable tradesmenable to install the model of their choice.

4. Develop the right products

The marketing system, not the latrinedesign, is the key to the success of any

sanitation program, but without appropriateproducts it will fail. Defecation is privateand sensitive behavior; families are alldifferent and need product choices thatmeet their different needs. Producers ofsanitation are usually small scale builders,who operate informally and lack thecapacity and resources to develop newproducts on their own. Government canafford to make this initial investment.

Top-down sanitation programs usually startwith a sanitation technology which thepromoters see as a ‘solution’ to a problemdefined by ‘outside experts’. This has oftenled to the promotion of technology which isunaffordable and inappropriate. Instead, itis wiser to make the effort to understandthe problems experienced and defined bythe poor, and then seek solutions whichpeople need and want.

Small scale producers play an important role in meeting demand for the local sanitation market.Photo credit: Andreas Knapp

Page 11: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

The Case forMarketing Sanitation

Developing suitable products requires adifferent approach from that adopted bymost sanitation engineers. Instead ofdesigning to a minimum specification, toiletproducts should be designed to a targetprice, for a market niche. If the design istoo expensive, the technical specificationneeds revising so as to reduce the cost.

5. Develop a thriving industry

Building consumer demand will generatemore ‘pull’ in the market. Measures togenerate more ‘push’ include capacity-building through training, credit and otherservices for small businesses. Continuingresearch is also needed, to monitor theevolving market.

The interests of the public and privatesectors are not identical. The first concernof the public bodies involved is to extendaccess to those who currently lack evenbasic sanitation. There is, however, noobligation on private providers to meet theneeds of the poor if more prosperoushouseholds offer greater returns. Constantmonitoring of the working of the market isneeded to ensure that public efforts andresources invested in the sector continue tobenefit the unserved, and not only theprivileged.

6. Regulate waste transportand final disposal

Many low-cost latrine types are on-sitesystems, disposing of the excreta into ahole in the ground; these include pit latrinesand pour-flush toilets. They are sustainableonly if a new pit can be dug when the oldone is full, or if a pit emptying service isavailable. Consumer studies (Jenkins 2004)have found that the limited lifetime of such

latrines is an important constraint todemand for home sanitation.

In many cities, deficient pit emptying is amajor constraint to the adoption and use ofpit latrines, a cause of disease in those whoundertake the task, and a major source ofenvironmental pollution.

A case for public subsidy and regulation ofthe disposal of wastes outside the homecan therefore be established. Ifcoordinated to work well with the privately-provided home sanitation productspromoted through marketing, this will makehome sanitation more attractive, as

The private sector can provide affordable pit emptying services.Photo credit: WSP-AF

affordable pit emptying services extend thelife of the household’s investment.

Summary

In summary, the marketing of sanitationoffers a whole new approach to ensuringthat people get toilets. This impliesrethinking the role of the public sector, sothat it harnesses the power of the marketand helps it to do its job. The market is themost suitable vehicle to get us to themillennium sanitation goal. Governmentneeds to take the brakes off, oil its wheels,and of course, to steer it.

Page 12: Marketing Sanitation 4 - World Banksiteresources.worldbank.org/.../case_marketing_sanitation.pdf · Marketing Sanitation Access to sanitation – the hygienic disposal of human excreta

August 2004

0%1�2 %% 345

To help the poor gain sustainedaccess to improved water andsanitation services.

0%1�674$ 4��1#8�498%5

The Governments of Australia, Austria, Belgium,Canada, Denmark, Germany, Italy, Japan,Luxembourg, the Netherlands, Norway, Sweden,Switzerland, and the United Kingdom, The UnitedNations Development Programme, andThe World Bank.

#,:430�9$�9294�%5

This review paper has been prepared by ProfessorSandy Cairncross. It draws on the long and richexperience of many colleagues at the Water andSanitation Program-Africa Region. The paper waspeer reviewed by Peter J. Kolsky, Ousseynou Diopand Valerie Curtis. Detailed feedback was alsoprovided by Piers Cross, Belinda Calaguas and TimWilliamson. While these colleagues have helped inimproving the overall reasoning of the paper, theresponsibility for any errors of omission andinterpretation remain with the authors. The authorswould like to thank Toni Sittoni and Andreas Knappfor their editorial guidance.

Cover photo: Barry Jackson.Design & layout: Kul Graphics Ltd.

Water and Sanitation Program -

Africa

World BankHill Park BuildingUpper Hill RoadPO Box 30577NairobiKenya

Phone: +254 20 322-6306Fax: +254 20 322-6386E-mail: [email protected]: www.wsp.org

ABOUT THE SERIESWSP Field Notes describe and analyze projects and activities in water and sanitationthat provide lessons for sector leaders, administrators, and individuals tackling the waterand sanitation challenges in urban and rural areas. The criteria for selection of storiesincluded in this series are large-scale impact, demonstrable sustainability, good costrecovery, replicable conditions, and leadership.

#������ ������� ����� ��� � ����

(;;)�������������� �������

�����������������������$����

%��������(;;)�!����<�4���)���

���������������"��"��&<�)"�=���

,������� �%�������<<(����������������

����������������������������������

��������0��������%��������$������

1�����4���<��0��������$,5�����0����

����������������"����������"

����������$���������

������ �2��������(;;;���� ���������

����������������������������

��������!�6�����4����4���$����5�0���

>�%��������1�������?�%����#���

����������"����������"

�@������������

���� �#���<<=��"��#����������������

(���9����� �4���A���5��������2���� ���

B����� �2��(;;C���������������������

��� ��������������!

2�:�� �4������<<(��������"�$���%��������

������"��#�����������������

&���������������������

&�������������1����� �2������5

%����������0����>�%��������1������

?�%����#�����<<<�

&�����&�����������"��������

'����������������������'�������������

�����"�������������(�$��'����!

���1������4���$����5�0����>

%��������1�������?�%����#������

$6 $�

0����>�%��������1�������?�%����#���

(;;;��"��#����������������������'����!

6�����4����4���$����5�0����>�%�������

1�������?�%����#�������0����#���

0�������� �4��:���<<<��)�������������

"��#������*�����$������+�����

��������3�� �,#5�%����1���������

References and further reading


Recommended