IT'S an idea that goes back to the fourth century BC, and it still works. In his play Lysistrata, Aristophanes imagined a group of Athenian women, who were tired of endless wars, agreeing to withhold sexual favours from their husbands and lovers until they stopped the fighting. The Latinos and their supporters in the United States who demonstrated against the system that needs their labour but refuses to give them citizenship were using a version of the Athenian women's protest: take away what you take for granted and you come to value it more. “A Day Without Immigrants” brought hundreds of thousands on to the streets of America's cities and emptied the kitchens of restaurants and the farms; others protested simply by staying away from work or school. After decades of benign neglect of its illegal immigration problem, the United States has some 11 million workers who lack proper papers and have no prospect of getting citizenship. As Monday's demonstrations showed, if they were all to be sent home, as some lobbyists argue they should be, many of America's essential services would come to a halt. President Bush is opposed to deportation of the illegals and wants to give them guest-worker status, but legislation currently before Congress would change their presence in the country from a misdemeanour to a crime. Many business interests believe that the immigrants are essential to the nation's economy and that a way should be found to let them remain while strenghening border controls to regulate future entry. The U.S. faces a seemingly insoluble dilemma.