**Conjecture**Every simple graph on five or more vertices is switching-reconstructible.

To *switch* a vertex of a simple graph is to exchange its sets of neighbours and non-neighbours. The graph so obtained is called a *switching* of the graph. The collection of switchings of a graph G is called the *switching deck* of . A graph is *switching-reconstructible* if every graph with the same deck as is isomorphic to .

There are four pairs of non-isomorphic graphs of order with the same switching deck. One of them consists of the empty graph and the -cycle.

Stanley [S] proved that a graph on vertices is switching-reconstructible if .

An analogous problem was posed for digraphs. Instead of complementing the edges at a vertex, one reverses each of its incident arc.

## Bibliography

*[S] R. P. Stanley Reconstruction from vertex-switching. J. Combin. Theory Ser. B, 38 (1985), 132--138.

* indicates original appearance(s) of problem.