theorem Th20:
  m in Maps(A,B) implies m`2 in Funcs(A,B)
proof
  assume
A1: m in Maps(A,B);
  then
A2: m = [[A,B],m`2] by Th16;
  then
A3: m`2 is Function of A,B by A1,Lm4;
  B = {} implies A = {} by A1,A2,Lm4;
  hence thesis by A3,FUNCT_2:8;
end;
