No need to tie forward

[jasonreich]

If we're using equivalence then the 'future' state will be able to tie back to this one.

[jasonreich]

Quickly hacking in isJust $ Map.lookup i_prev (scDefinition scpSt) didn't work. Looks like it caused non-termination but hard to tell.

[jasonreich]

Perhaps it is due to equivalence being broken?

[jasonreich]

Nope. Fixed equivalence and it still fails to terminate. OH! It can't fold on recursive ones.

[jasonreich]

Wasn't that either, hmmmm.