Phil Bloomer of Oxfam is right to concentrate on the effects of the recession on the world's poorest ("No green shoots for poor countries", 20 September). He is especially right to endorse French President Nicolas Sarkozy's proposal for a special tax on currency transactions.
Ever since the ending of the US dollar's convertibility to gold in 1971, and the break-up of the Bretton Woods system of fixed currencies, global currency markets have been free to buy and sell national currencies without hindrance. The threat of their currency being either overvalued or undervalued, has meant that governments have not been able to run deficits (with the exception of the United States) to finance spending on education and health. Currency markets have been effectively able to dictate economic and social policy to entire countries.
If the Tobin tax can discourage such currency speculation, it would free countries to spend once again more on their social and economic development.
A tax on currency transactions designed to raise $30-50bn would be fortunate to raise $3-5bn per annum: banks would find ways round it. There is a much larger pot of money available to poor countries much closer to home. The African Union has calculated that $150bn drains out of the continent every year through corruption. If African governments started to implement policies on good governance while cracking down on corruption, progress in reducing poverty on the continent would be colossal.
High Wycombe, Buckinghamshire
The president of Yemen, Ali Abdullah Saleh, is from an area historically Zaidi ("The land with more guns than people", 20 September). Zaidism is a very early form of Shiism – completely distinct from the branch of Shiism known as Twelver, of Iran and Iraq. It is legally close to Sunnism but philosophically and intellectually open to debate in a manner inadmissible in Saudi Sunni Wahhabism.
As a military autocrat and not a religious figure, Saleh and his Congress party built power in an alliance with the late Sheikh Abdullah al-Ahmar, head of the Hashid confederation, and his Islah party closely tied to Saudi Arabia. Thus, it is false to portray the conflict as Sunni versus Shia.
Furthermore, Hashed and Bakil are not "tribes" but confederations of tribes of a contractual and political nature. And "khat" ( Catha edulis) is not a narcotic; it is an amphetamine with mild hallucinogenic qualities, and not on the international list of narcotics.
These are important distinctions to make in reporting on the tragedy unfolding in North Yemen.
Professor of Anthropology London School of Economics
Whilst as you rightly claim the Liberal Democrats have long been by far the most sincerely green of the main parties ("Lib Dems: Credit where it's due", 20 September), they so far lack substantive policies to fund vital technological research. If they are to enter the election on a mandate of ushering in a truly green technological revolution, they must recognise that this revolution has to be primarily led by government. If they make the error of over-relying on venture capital, they are merely picking up litter and insulating lofts.
Janet Street-Porter's report that the Tories would close BBC4 raises great concerns ("A slimmer Auntie would be even more attractive", 20 September). This channel is a shining light in bringing us intelligent programmes instead of the puerile dross shown on many of the mainstream channels. Surely the content on BBC4 is exactly what the BBC charter calls for.
Nicholas Taleb did not coin the term "black swan" (Interview, 20 September). It was the Roman poet Juvenal (around AD100) who came up with the term: "rara avis in terris nigroque simillima cycno" – "a rare bird anywhere and very similar to a black swan" (Satire 6, line 165). He was writing about the likelihood of finding a perfect wife.
Bury St Edmunds, Suffolk
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