reserve a,b for Complex;
reserve V,X,Y for ComplexLinearSpace;
reserve u,u1,u2,v,v1,v2 for VECTOR of V;
reserve z,z1,z2 for Complex;

theorem Th6:
  z * (- v) = (- z) * v
proof
  thus z * (- v) = z * ((- 1r) * v) by Th3
    .= (z *(- 1r)) * v by Def4
    .= (- z) * v;
end;
