Expand the definition of a "simple" farkas proof.

Expand the definition of a "simple" farkas proof.

Before, a "simple farkas proof" was one that just applied the farkas
lemma.

Now it allows for the antecedents to (optionally) be tightened.

Note that hasSimpleFarkasProof was (and is) dead code.

We will use it to decide whether to print a proof or a hole.