function checkear_numero(e) {
    var keynum;
    var keychar;
    var numcheck;
    if(window.event) // IE
      {
      keynum = e.keyCode;
      }
    else if(e.which) // Netscape/Firefox/Opera
      {
      keynum = e.which;
      }
    keychar = String.fromCharCode(keynum);
    numcheck = /\d|\010/;
    return numcheck.test(keychar);
  };
  function checkear_float(e) {
    var keynum;
    var keychar;
    var numcheck;
    if(window.event) // IE
      {
      keynum = e.keyCode;
      }
    else if(e.which) // Netscape/Firefox/Opera
      {
      keynum = e.which;
      }
    keychar = String.fromCharCode(keynum);
    numcheck = /\d|\010|\055|\056/;
    return numcheck.test(keychar);
  };
  function checkear_letras(e) {
    var keynum;
    var keychar;
    var numcheck;
    if(window.event) // IE
      {
      keynum = e.keyCode;
      }
    else if(e.which) // Netscape/Firefox/Opera
      {
      keynum = e.which;
      }
    keychar = String.fromCharCode(keynum);
    numcheck = /[1-9]|[a-z]|[A-Z]|\010/;
    return numcheck.test(keychar);
  };