 [semidet]min_of_heap(+Heap, 
?Key1, ?Value1, ?Key2, ?Value2)Gets the two minimum-priority elements from Heap. Complexity: 
logarithmic (amortized).
[semidet]min_of_heap(+Heap, 
?Key1, ?Value1, ?Key2, ?Value2)Gets the two minimum-priority elements from Heap. Complexity: 
logarithmic (amortized).
- bug
- This predicate is extremely inefficient and exists for compatibility 
with earlier implementations of this library and SICStus compatibility. 
It performs a linear amount of work in the worst case that a following 
get_from_heap has to re-do.