Adding a todo list
Checkpoint: preparing to add fold on var context
Checkpoint: addind a fold on var context (cont.)
Generalize the variables whose type depends on variables that occurs
in the type of the term we destruct (todo: do the same thing for the
conclusion!)
Generalized variables that occur in the diagonalization, in the same
fashion as we generalize the rel-context.
Re-generalize variables that occurs (in the same fashion as we handle
rels).