test for undefined variables & renaming variables

Q: Does anyone know of a way to test for undefined variables? For example, I am sending a variable into the page, but the processing of the page depends on what is being passed to the page. Say, I am typing the following on the location bar: index.php?fuseaction=something&fuse=6 and I want something to happen if fuse is actually declared, and something else to happen if fuse is not defined. I have tried isdef(), but that function does not seem to work, and I couldn't find it in the manual when I was looking for it. Code to use on: if($HTTP_GET_VARS("fuse") == NULL) then do something; else do something else; Q: Also, does anyone know how to rename a variable? I want to create a variable $attributes_NameOfVariable, but it does not seem to work. is there a function that exists in PHP that will assist me in this process? Thank you for all of your help, and thank you for your time, August Malson