theorem
  f1 is total & f2^ is total implies (f1/f2).c = f1.c *(f2.c)"
proof
  assume that
A1: f1 is total and
A2: f2^ is total;
A3: f2 is total by A2,Th54;
  f2"{0} = {} by A2,Th54;
  then f1/f2 is total by A1,A3,Th55;
  then dom (f1/f2) = C;
  hence thesis by Def1;
end;
