listminus := proc (L1::list, L2::list) options `Maple Advisor Database 1.01 for Maple 6`, `Copyright (c) 2000 by Robert B. Israel. All rights reserved`; local res, a, i; res:= L1; for a in L2 do if member(a,res,'i') then res:= subsop(i=NULL,res) fi od; res end;