How can I tell programmatically if a function has evaluated in a nontrivial way?
I'd like to do, essentially, something along the lines of
f[x]===HoldForm[f[x]], a test that returns true if
f[x] just evaluates to
f[x] because it's not defined, or else false if
f[x] actually does something. Of course, that example code doesn't work - my guess is that the HoldForm is printing itself or something.