# Reconstruction conjecture

The *deck* of a graph is the multiset consisting of all unlabelled subgraphs obtained from by deleting a vertex in all possible ways (counted according to multiplicity).

**Conjecture**If two graphs on vertices have the same deck, then they are isomorphic.

See Wikipedia's Reconstruction Conjecture for more on this problem.

## Bibliography

*[K] P. J. Kelly, A congruence theorem for trees, Pacific J. Math., 7 (1957), 961–968.

*[U] S. M. Ulam, A collection of mathematical problems, Wiley, New York, 1960.

* indicates original appearance(s) of problem.

### correction and partial results

On May 23rd, 2008 melch says:

this should be on 3 or more vertices. False for digraphs, hypergraphs, and infinite graphs. It is open for simple graphs and multigraphs

## A strategy for simple graphs?

How about 1) Prove for a 4-node, or tetrahedral graph. 2) Demonstrate that all graphs with > 4 nodes are composed of multiple overlapping tetrahedrons 3) Figure out how coupled tetrahedra function when nodes are deleted. 4) Induct on number of tetrahedra in graph. ?

Obviously (3) is the tough part, but why should it be impossible?