m Joseph T. Travaline, Burlington, Mass., was on brief, for defendant, appel- lant. Diane M. Kottmyer, Boston, Mass., with whom Ernest S. Dinisco, Jane E. Serene, Sp. Attys., William F. Weld, U.S. Atty. and Jeremiah T. O'Sullivan, Sp. Atty., Boston, Mass., were on brief, for appellee. Before BREYER, ALDRIC