🚀 go-pugleaf

In article <29700028@uiucdcs> reddy@uiucdcs.UUCP writes:
>
>To rggoebel@watdragon:
>
>You can try explaining cut, var and nonvar logically.  If you do it
>successfully, you could become a star of the logic programming community.

In all humility, and with a strong chance of getting it all wrong here I
go:

var(X) = All t in Term: can_unify(t,X)

where can_unify is true if a most general unifier can be found for both
its arguments.

nonvar(X) = Exists t in Term: NOT(can_unify(t,X))

Dirty structures like lists with uninstantiated tails (as in the unit
time queue trick) are nonvar under these definitions.

I've had minimal training in Logic, so I don't know if the set of all
Terms is an ok construct. Seems ok to me. 

This leaves cut, which is definitely meta-logical.