theorem
  (i|->c1) - (i|->c2) = i|->(c1-c2)
proof
  reconsider s1=c1, s2=c2 as Element of COMPLEX by XCMPLX_0:def 2;
  (i|->s1) - (i|->s2) = i|->(diffcomplex.(s1,s2)) by FINSEQOP:17
                     .= i|->(c1-c2) by BINOP_2:def 4;
  hence thesis;
end;
