theorem Th9:
  (cod m <> {} or dom m = {}) & m`2 is Function of dom m,cod m
proof
  consider f, A,B such that
A1: m = [[A,B],f] and
A2: ( B = {} implies A = {})& f is Function of A,B by Th4;
  thus thesis by A1,A2;
end;
