How to know when mc is running in a terminal

[Mike Smithson]

I have a specialized F4 script ($EDITOR) that I need
to know whether my editor is being called from mc or
not.

The MC_ env vars don't seem to exist when F4 is hit.

Question: how can a script know whether it is being
called from F4 in mc or just a terminal?

Thanks in advance.

-- 
Peace and Cheer