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
  (- z) * (- v) = z * v
proof
  thus (- z) * (- v) = (- (- z)) * v by Th6
    .= z * v;
end;
