create or replace FUNCTION F_COMPROBARDNI
(
  NIF IN VARCHAR2
) RETURN BOOLEAN AS
vLetra VARCHAR2(5);

BEGIN
  vLetra := SUBSTR(NIF, -1, 1);
  RETURN F_LETRADNI(SUBSTR(NIF, 1,LENGTH(NIF)-1))=vLetra;
END F_COMPROBARDNI;