theorem
  <*c1*> - <*c2*> = <*c1-c2*>
proof
  reconsider s1=c1, s2=c2 as Element of COMPLEX by XCMPLX_0:def 2;
  <*s1*> - <*s2*> = <*diffcomplex.(s1,s2)*> by FINSEQ_2:74
                 .= <*c1-c2*> by BINOP_2:def 4;
  hence thesis;
end;
