theorem Th1: :: singleUsed
  UsedILoc(l .--> i) = UsedIntLoc i
proof rng(l .--> i) = {i} by FUNCOP_1:8;
  hence UsedILoc(l .--> i) =  union { UsedIntLoc i1 : i1 in {i} }
       .= UsedIntLoc i from SUBSET_1:sch 5;
end;
