The law firms of Baker & McKenzie and Macdonald, Halsted & Laybourne announced that they are engaged in merger discussions . . . Madison, N.J.-based Schering-Plough Corp., a pharmaceutical and consumer products company, said it has agreed to buy Cooper Cos.' worldwide contact lens business for about $150 million . . . The New York Mercantile Exchange has delayed making any decision about a possible merger with the Commodity Exchange, said Comex President Alan J. Brody . . . The Investment Company Institute reported that the assets of the nation's 415 money market mutual funds rose $1.22 billion in the week ended Jan. 27 . . . General Motors' Chevrolet division is offering a $1,200 rebate on three Nova models to owners of imported cars. A $600 rebate is available to owners of domestic cars. Both programs end Feb. 29 . . . Stop & Shop Cos. said its board rejected Dart Group's $30 per share cash takeover offer.