reserve a, b, c, d, e for Complex;

theorem :: REAL_2'93
  c <> 0 implies a - b = c * (a / c - b / c)
proof
  assume
A1: c<>0;
  hence a-b=c*(a/c)-b by Lm3
    .=c*(a/c)-c*(b/c) by A1,Lm3
    .=c*(a/c-b/c);
end;
