hort validNomencalture(long number, long pto )
{
    short retour = 1;
    FILE *pf = fopen(F_EXAMEN,"rb");
    Examen Exam ;

    if(pf != NULL)
    {
        if( fseek(pf,pto,SEEK_SET) == 0 &&  (fread(&Exam,(long)sizeof(Examen),1,pf)  == 1) )
        {
                while(retour == 1 && Exam.nomenclature != -1)
                {
                    if(Exam.nomenclature == number)
                        retour = 0;
                    if(fseek(pf,Exam.offsetSvt,SEEK_SET) != 0 && fread(&Exam,sizeof(Examen),1,pf) != 1 )
                        retour = 0;
                }
        }
         else
                retour = 0;
      }


    if(!retour)
        printf("Erreur lecture du fichier %s\n",F_EXAMEN);

    return retour;
}