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

theorem :: REAL_2'77
  c <> 0 & d <> 0 & a * c = b / d implies a * d = b / c
proof
  assume that
A1: c<>0 and
A2: d<>0;
  assume a*c =b/d;
  then a*c*d=b by A2,Lm3;
  then a*d*c =b;
  hence thesis by A1,Lm9;
end;
