SWI-Prolog -- library(heaps)

add_to_heap/4	Adds Key with priority Priority to Heap0, constructing a new heap in Heap.
delete_from_heap/4	Deletes Key from Heap0, leaving its priority in Priority and the resulting data structure in Heap.
empty_heap/1	True if Heap is an empty heap.
get_from_heap/4	Retrieves the minimum-priority pair Priority-Key from Heap0.
heap_size/2	Determines the number of elements in Heap.
heap_to_list/2	Constructs a list List of Priority-Element terms, ordered by (ascending) priority.
is_heap/1	Returns true if X is a heap.
list_to_heap/2	If List is a list of Priority-Element terms, constructs a heap out of List.
merge_heaps/3	Merge the two heaps Heap0 and Heap1 in Heap.
min_of_heap/3	Unifies Key with the minimum-priority element of Heap and Priority with its priority value.
min_of_heap/5	Gets the two minimum-priority elements from Heap.
singleton_heap/3	True if Heap is a heap with the single element Priority-Key.