The pressing game on black-and-white graphs is the following: given a graph
with its vertices colored with black and white, any black vertex
can be pressed, which has the following effect: (1) all neighbors of
change
color; i.e., white neighbors become black and vice versa; (2) all pairs of neighbors of
change
adjacency; i.e., adjacent pairs become nonadjacent and nonadjacent ones become adjacent;
and (3)
becomes a separated white vertex. The aim of the game is to transform
into an all-white, empty graph. It is a known result that the all-white
empty graph is reachable in the pressing game if each component of
contains
at least one black vertex, and for a fixed graph, any successful transformation has the
same number of pressed vertices.
The pressing game conjecture states that any successful pressing sequence can be
transformed into any other successful pressing sequence with small alterations. Here
we prove the conjecture for linear graphs, also known as paths. The connection to
genome rearrangement and sorting signed permutations with reversals is also
discussed.
Keywords
bioinformatics, sorting by reversals, pressing game,
irreducible Markov chain