function submitProdFrm(frmName)
  { var frm = document.forms[frmName];
    if( frm )
    { var mnozstvi = 1;
      var koef     = 1;
      
      if( frm['_mn'])        mnozstvi = Number(frm['_mn'].value);
      if( frm['_koef'] )     koef     = Number(frm['_koef'].value);
      if( frm['mnozstvi'] )  frm['mnozstvi'].value = Number(mnozstvi*koef);
      
      frm.submit();
    } 
  }