reserve w, w1, w2 for Element of ExtREAL;
reserve c, c1, c2 for Complex;
reserve A, B, C, D for complex-membered set;
reserve F, G, H, I for ext-real-membered set;
reserve a, b, s, t, z for Complex;
reserve f, g, h, i, j for ExtReal;
reserve r for Real;
reserve e for set;

theorem
  F c= G & H c= I implies F///H c= G///I
proof
  assume
A1: F c= G & H c= I;
  let i;
A2: F///H = {w1/w2: w1 in F & w2 in H} by Th101;
  assume i in F///H;
  then ex w,w1 st i = w/w1 & w in F & w1 in H by A2;
  hence thesis by A1,Th102;
end;
