<form name="form1" action="http://www.3dzhimo.com" method="get">
<input name=aa id="abc" onkeyup="form2.bcd.value=value">
</form>
<form name="form2" action="http://www.123.com" method="get">
<input name=aa id="bcd" onkeyup="form1.abc.value=value">
</form>
<input name=aa id="abc" onkeyup="form2.bcd.value=value">
</form>
<form name="form2" action="http://www.123.com" method="get">
<input name=aa id="bcd" onkeyup="form1.abc.value=value">
</form>
<input name=aa id="abc" onkeyup="document.getElementById('bcd').value=this.value">
</form>
<form action="http://www.123.com" method="get">
<input name=aa id="bcd" onkeyup="document.getElementById('abc').value=this.value">
</form>