Hiding <FORM> Variables

Here are two sample lines for report type of either open or closed.

<INPUT TYPE="hidden" NAME="call_type" VALUE="open">
<INPUT TYPE="hidden" NAME="call_type" VALUE="closed">

These are mutually exclusive options. Could also be independent:

<INPUT TYPE="hidden" NAME="open_call" VALUE="yes">
<INPUT TYPE="hidden" NAME="close_call" VALUE="yes">

but I don't like that approach.