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 Th224:
  F///f = {w/f: w in F}
proof
  thus F///f c= {w/f: w in F}
  proof
    let e be object;
    assume e in F///f;
    then consider w1,w2 such that
A1: e = w1*w2 & w1 in F and
A2: w2 in {f}"";
    consider w3 being Element of ExtREAL such that
A3: w2 = w3" and
A4: w3 in {f} by A2;
    w1*w3" = w1/w3 & w3 = f by A4,TARSKI:def 1;
    hence thesis by A1,A3;
  end;
  let e be object;
  assume e in {w/f: w in F};
  then ex w st e = w/f & w in F;
  hence thesis by Th223;
end;
