Things in Chapter 9 my program can't (yet) do
---------------------------------------------

The things I can't yet do: functional relations, i.e. substituting f(a) for a in 
f(a) to get f(f(a)). So there's an example in the text:

     1. f(a) = b
     2. f(b) = a
     3. f(f(a)) = a.

I think this is something like saying, in aRb (or subject-predicate, or infix) 
syntax:

The brother of Pat is Quincy.
The brother of Quincy is Pat.
Who is the brother of the brother of Quincy? => Pat.

My system can't yet do these types of nested substitutions.

Another thing I can't yet do is disjunctions (a or b) and conjunctions (a and b).

I think adding "or" and "and" shouldn't be too difficult, in fact I've played 
around with it in other versions of logicagent.