Type of priority queues.

create ~dummy c creates a new heap, with initial capacity of c. The value dummy is used to fill unused cells of the internal array. Note: dummy can still be used as a regular value in the queue.

length h returns the number of elements of h

is_empty h checks the emptiness of h

add x h adds a new element x in heap h; size of h is doubled when maximum capacity is reached; complexity $O(log(n))$

minimum h returns the minimum element of h; raises Empty when h is empty; complexity $O(1)$

remove h removes the minimum element of h; raises Empty when h is empty; complexity $O(log(n))$

pop_minimum h removes the minimum element of h and returns it; raises Empty when h is empty; complexity $O(log(n))$

usual iterators and combinators; elements are presented in arbitrary order