# What is/How to do Unification

I'm reviewing for a final exam on Monday, and I have a question I was unable to answer on a previous test. The professor's notes were horrendous, and I can't find anything better online. They all seem to talk way over my head.

For each of the following pairs of literals, determine whether or not they are unifiable. If they do, show the unifiers.

1. P(a), Q(g(x))
2. P(x), Q(g(a))

I have a feeling that it's insanely easy, as the prof (despite teaching horribly, gives easy enough questions) but I still have no idea what to do.

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"The professor's notes were horrendous, and I can't find anything better online." I'm a dinosaur, but can't help thinking "Try your university library. Look at a book or two ...". –  Peter Smith Dec 9 '12 at 12:06
@PeterSmith I've seen a couple of textbooks, and they don't seem to help me at all either. They explain things in a way that is far too technical for me to grasp. I need examples of how to apply the algorithm, not just the algorithm. –  agent154 Dec 9 '12 at 19:52

There is no unification in either case, since whatever you substitute for $x$ (and perhaps $a$; you didn't state which symbols are variables to be substituted), the first expression of the pair will have $P$ as its outermost symbol and the second one will have $Q$.