The little object that wasn't there

[Cal Horner]

I have a stack (like everyone else) and the 'Master' card contains all the
objects needed to make a complete window.

Some of the buttons are needed for separate cards, but not all of the cards.
When I need one I do the standard thing, push -> go to master card -> copy
one of the buttons -> pop -> paste. Works a treat.

Here's my problem: 

How do I, programatically, check to see if the button exists, before I do
the standard thing?

And how do I check for an existing button - programatically - before I
delete a button that isn't there?

Surely there must be a command that handles that.

Cal