PPrinter.ComparatorNode comparator
val is_eq : Region_pp_intf.comparison -> boolReturns true iff comparison is Equivalent
val compare : node -> node -> Region_pp_intf.comparisonCompare node1 with node2
val compare_all : node list -> node list -> Region_pp_intf.comparisonCompare each element of nodes1 with the matching element of nodes2. If lengths don't match return UnComparable