Alpha 137b release notes
=========================

Change
=======
As suggested by Rubén, if filter is passed to vu-narrow, filtered variant narrowing
is used rather than variant narrowing for the final unification with the goal, rather
than just the narrowing steps. For example:

mod NARROWING-VENDING-MACHINE is
   sorts Coin Item Marking Money State .
   subsort Coin < Money .
   op empty : -> Money .
   op __ : Money Money -> Money [assoc comm id: empty] .
   subsort Money Item < Marking .
   op __ : Marking Marking -> Marking [assoc comm id: empty] .
   op <_> : Marking -> State .
   ops $ q : -> Coin .
   ops a c : -> Item .
   var M : Marking .
   rl [buy-c] : < M $ > => < M c > [narrowing] .
   rl [buy-a] : < M $ > => < M a q > [narrowing] .
   eq [change] : q q q q M = $ M [variant] .
endm

vu-narrow {filter,delay} < X:Money > =>1 S:State .

now only produces two solutions, with what used to be the third solution being
subsumed by the second solution due to filtering the variant unifiers.
