Hi, I'm using a mutable heap, in particular a mutable d_ary_heap, for the priority queue in Djikstra's algorithm. When does a handle become invalid? I don't know how a d_ary_heap is implemented, but if it's like the standard array-backed binary heap, then I would expect invalidation of many handles whenever an item gets popped or an item gets increased or decreased. I need references to the elements in order to update them, so if the invalidation I expect does happen as I describe, how can I get permanent references/pointers/iterators to the elements? Perhaps another implementation besides d_ary_heap? Although I haven't profiled the performance, I think even though something like the fibonacci heap may have permanent handles, pointer chasing, more frequent cache misses and frequent dynamic memory allocation may be detrimental to performance. Which heap implementation supports key increase without handle invalidation? Josh