Scratch space for notes about curtailment



all results must track curtails
 - done

when merging two results that have curtails for the same combinator, use the smaller curtail
 - done

when updating a result, replace the curtails with the leftrec level for the current context
 - done

ignore a previous result when the current leftrec level is less than the previous result curtail level for even one of the curtails
 - done

the function to check if reusable needs to take into account a +1 for the combinator being currently memoized
 - done