theorem Th1:
  (s/t)*(u*x)=(s*u)/t*x & (1/t)*(u*x)= u/t*x
proof
  thus (s/t)*(u*x) = ((s/t)*u)*x by EUCLID_4:4
    .= (s*u)/t*x by XCMPLX_1:74;
  thus (1/t)*(u*x) = ((1/t)*u)*x by EUCLID_4:4
    .= u/t*x by XCMPLX_1:99;
end;
