improve crossProduct
some progress, maybe
subst and env work again
subst and env work again
almost works
Grouped reduction works
del legacy
try parallel rule matching
parallel nondeterm semantics works
true parallel semantics
clarify closures
bit of cleanup
refactor
more refactor
refactor parallel nondeterm
refactorings
refactor nondeterm_parallel
refactor concurrent
flat syntax for sem 1
emphasize values