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
  a <> 0 implies a /// (A\B) = (a///A) \ (a///B)
proof
  assume
A1: a <> 0;
  thus a /// (A\B) = a ** ((A"")\(B"")) by Th34
    .= (a**(A"")) \ (a**(B"")) by A1,Th199
    .= (a///A) \ (a///B);
end;
