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

theorem :: REAL_2'95
  c <> 0 implies a - b = (a * c - b * c) / c
proof
  assume
A1: c<>0;
  thus a-b=a+-b .=(a*c+(-b)*c)/c by A1,Th115
    .=(a*c-b*c)/c;
end;
