F.2.42 library(pairs)

group_pairs_by_key/2	Group values with equivalent (==/2) consecutive keys.
map_list_to_pairs/3	Create a Key-Value list by mapping each element of List.
pairs_keys/2	Remove the values from a list of Key-Value pairs.
pairs_keys_values/3	True if Keys holds the keys of Pairs and Values the values.
pairs_values/2	Remove the keys from a list of Key-Value pairs.
transpose_pairs/2	Swap Key-Value to Value-Key.