Math & Science ⇒ \qedhere -- replicating functionality

[archels]

Hello,

I am using a predefined stylesheet which defines various environments like {definition}, {proof}, {lemma}, etc. I want to add a little box symbol to the end of each of these environments.
I run into the problem that if the last element of these environments is an {align} or an {equation} or so, the box symbol appears on the next line. This issue has been addressed (and, apparently, solved) in amsthm, which defines an environment--with box--for proofs.
However, using this package conflicts with my predefined styles. Looking at the source of amsthm, I couldn't make heads or tails of it--guess I'm still a LaTeX newbie!
Could someone possibly direct me on how to replicate the \qedhere behaviour, i.e. box symbol on the same line even when the proof environment ends with an align or equation or so?

Many thanks!

[daleif]

Why don't you just use ntheorem instead?