Further inspection predicates of an association list and its elements 
are:
- [semidet]is_assoc(+Assoc)
- True if Assoc is an association list. This predicate checks 
that the structure is valid, elements are in order, and tree is balanced 
to the extent guaranteed by AVL trees. I.e., branches of each subtree 
differ in depth by at most 1. Does not validate that keys are 
sufficiently instantiated to ensure the tree remains valid if a key is 
further instantiated.
- [semidet]map_assoc(:Pred, 
+Assoc)
- True if Pred(Value) is true for all values in Assoc.
- [semidet]map_assoc(:Pred, 
+Assoc0, ?Assoc)
- Map corresponding values. True if Assoc is Assoc0 
with Pred applied to all corresponding pairs of of values.