Descrizione2SAT median graph.svg	A median graph representing the set of solutions to a 2-satisfiability instance
Data	2 maggio 2008
Fonte	Opera propria
Autore	David Eppstein
Licenza (Riusare questo file)	Public domainPublic domainfalsefalse Io, detentore del copyright su quest'opera, la rilascio nel pubblico dominio. Questa norma si applica in tutto il mondo. In alcuni paesi questo potrebbe non essere legalmente possibile. In tal caso: Garantisco a chiunque il diritto di utilizzare quest'opera per qualsiasi scopo, senza alcuna condizione, a meno che tali condizioni siano richieste dalla legge.

Detailed description

This graph is formed from the 2-satisfiability instance

${\displaystyle \scriptstyle (x_{0}\lor x_{2})\land (x_{0}\lor \lnot x_{3})\land (x_{1}\lor \lnot x_{3})\land (x_{1}\lor \lnot x_{4})\land (x_{2}\lor \lnot x_{4})\land {} \atop \scriptstyle \quad (x_{0}\lor x_{5})\land (x_{1}\lor x_{5})\land (x_{2}\lor x_{5})\land (x_{3}\lor x_{6})\land (x_{4}\lor x_{6})\land (x_{5}\lor x_{6})}$

by creating a vertex for each satisfying truth assignment to the formula and an edge between any two assignments that differ in the value of a single variable. The vertices in the drawing are labeled by the sequence of variable values,

${\displaystyle \scriptstyle x_{0}x_{1}x_{2}x_{3}x_{4}x_{5}x_{6}.}$

In general, any 2-satisfiability instance has a set of solutions with the structure of a median graph, in which the median of any three solutions is formed by taking a majority vote separately for each variable's value. However, for some 2-satisfiability problems, the edges in this median graph may connect pairs of solutions that differ by simultanously flipping several variables that are forced by the instance to all be equal or unequal.