> Pebbling is a solitaire game played on an undirected graph $G$ , where > each vertex has zero or more pebbles. A single pebbling move consists > of removing two pebbles from a vertex $v$ and adding one pebble to an > arbitrary neighbor of $v$ . (Obviously, the vertex v must have at > least two pebbles before the move.) The PebbleDestruction problem > asks, given a graph $G = ( V; E )$ and a pebble count $p ( v )$ for > each vertex $v$ , whether there is a sequence of pebbling moves that > removes all but one pebble. Prove that PebbleDestruction is > NP-complete. First, I show that it is in NP since I can verify the solution in polynomial time, tracing back the pebble count from just one pebble. Next, what are some ideas on which problems to use as the basis for a polynomial-time reduction? Would something like vertex cover work? Or a vertex cover of different sizes? If so, how can it handle the varying number of pebbles on each move? Thank You. From: http://courses.engr.illinois.edu/cs473/sp2011/hw/disc/disc_14.pdf