theorem Th64: :: CARD_FIN:44
   n in dom cF implies Sum (cF|n) + cF.n = Sum (cF|(n+1))
proof
  assume
A1:  n in dom cF;
    reconsider cF as XFinSequence of COMPLEX;
 addcomplex.(addcomplex "**" cF|n, cF.n) = addcomplex "**" cF|(n+1)
      by Th42,A1;
  hence thesis by BINOP_2:def 3;
end;
