This is an implementation of a Fibonacci Heap. A Fibonacci Heap is
a very efficient heap. The cost of an insert is O(1), and the amortized
cost of an extract minimum is O(lgn). You can extract an already inserted
item out of order in O(lgn). The way the fibonacci heap obtains this is
by delaying the organizing of the items until you extract.

WWW: http://resnet.uoregon.edu/~gurney_j/jmpc/fib.html