A 60-year-old Walmart greeter will come up against the world's biggest retailer this week in another round of the largest sex discrimination case in history. In a case legal experts say will redefine discrimination law in the US, the supreme court will...begin hearing arguments why Betty Dukes and more than a million women who worked for Walmart between December 1998 and the present day should be able to sue the retailer in a class action. Walmart is appealing against an earlier court's decisions to let the case proceed after a judge said Dukes' lawyers had presented "significant proof of a corporate policy of discrimination". Walmart…says the case has spun out of control and threatens to cost the retailer billions of dollar if it is allowed to proceed....Some 20...major firms including General Electric and Microsoft have filed papers with the court in support of Walmart.