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///G)///H = F///(G**H)
proof
  thus (F///G)///H = F**((G"")**(H"")) by Th80
    .= F///(G**H) by Th85;
end;
