theorem
  for x,y being Variable of f holds f.(s, x/=y).x = s.x div s.y & for z
  st z <> x holds f.(s, x/=y).z = s.z
proof
  let x,y be Variable of f;
A1: x/=y = x/=.y;
  (.y).s = s.y by Th22;
  hence thesis by A1,Th46;
end;
