Would it be better to work with the command "isolate"

When defining:

isolate(gl1,z);

Maple tells the following:

"Error, (in isolate) invalid arguments for isolate"

Another idea:

would it be better to work with the command "isolate"?

When defining

isolate(gl1,z);

The message of maple is:

"Error, (in isolate) invalid arguments for isolate"