"All predicates in this subsection take a comparator argument, which is a comparator used to compare the values of the associations stored in the mappings. This comparator is used to define the equality of associations. Two associations are equal if and only if their keys and values are equal, respectively."

I was confused initially with the last sentence, until I realized "equal" for keys and values are different in terms of which comparator is used.  I think if I read carefully the current description isn't ambiguous, but how about something along this?

"All predicates in this subsection take a comparator argument, which is a comparator used to compare the values of the associations stored in the mappings.  Entries in the mappings are equal if their keys are equal with mappings' key comparator, and their values are equal with the given comparator.  Two associations are equal if and only if their entries are equal, respectively."