set of clauses:
{ ¬x1 ∨ x3 ∨ x4, ¬x2 ∨ x6 ∨ x4, ¬x2 ∨ ¬x6 ∨ ¬x3, ¬x4 ∨ ¬x2, x2 ∨ ¬x3 ∨ ¬x1, x2 ∨ x6 ∨ x3, x2 ∨ ¬x6 ∨ ¬x4, x1 ∨ x5, x1 ∨ x6, ¬x6 ∨ x3 ∨ ¬x5, x1 ∨ ¬x3 ∨ ¬x5 }
branch on x3
recursive call with x3=true
{
¬x1 ∨ x3 ∨ x4,
¬x2 ∨ x6 ∨ x4,
¬x2 ∨ ¬x6 ∨ ¬x3,
¬x4 ∨ ¬x2,
x2 ∨ ¬x3 ∨ ¬x1,
x2 ∨ x6 ∨ x3,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
¬x6 ∨ x3 ∨ ¬x5,
x1 ∨ ¬x3 ∨ ¬x5
}
=
{
¬x2 ∨ x6 ∨ x4,
¬x2 ∨ ¬x6,
¬x4 ∨ ¬x2,
x2 ∨ ¬x1,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
no contradiction, choose a branching variable
{
¬x2 ∨ x6 ∨ x4,
¬x2 ∨ ¬x6,
¬x4 ∨ ¬x2,
x2 ∨ ¬x1,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
{
¬x2 ∨ ¬x6,
¬x2,
x2 ∨ ¬x1,
x2 ∨ ¬x6,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
= (with ¬x2)
{
¬x2 ∨ ¬x6,
¬x2,
x2 ∨ ¬x1,
x2 ∨ ¬x6,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
{
¬x1,
¬x6,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
contradiction: ¬x1, ¬x6,
x1 ∨ x6
{
¬x2 ∨ x6 ∨ x4,
¬x2 ∨ ¬x6,
¬x4 ∨ ¬x2,
x2 ∨ ¬x1,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
{
¬x2 ∨ x6,
¬x2 ∨ ¬x6,
x2 ∨ ¬x1,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
no contradiction, no unit clause
{
¬x2 ∨ x6,
¬x2 ∨ ¬x6,
x2 ∨ ¬x1,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
{
x6,
¬x6,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
contradiction
{
¬x2 ∨ x6,
¬x2 ∨ ¬x6,
x2 ∨ ¬x1,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
=
{
¬x1,
x1 ∨ x5,
x1 ∨ x6,
x1 ∨ ¬x5
}
contradictin: from ¬x1 both x5 and ¬x5 follow
{
¬x1 ∨ x3 ∨ x4,
¬x2 ∨ x6 ∨ x4,
¬x2 ∨ ¬x6 ∨ ¬x3,
¬x4 ∨ ¬x2,
x2 ∨ ¬x3 ∨ ¬x1,
x2 ∨ x6 ∨ x3,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
¬x6 ∨ x3 ∨ ¬x5,
x1 ∨ ¬x3 ∨ ¬x5
}
=
{
¬x1 ∨ x4,
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
¬x6 ∨ ¬x5
}
no contradiction, no unit clause
{
¬x1 ∨ x4,
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
¬x6 ∨ ¬x5
}
=
{
x4,
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
¬x6 ∨ ¬x5
}
= (with x4=true)
{
x4,
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
¬x6 ∨ ¬x5
}
=
{
¬x2,
x2 ∨ x6,
x2 ∨ ¬x6,
¬x6 ∨ ¬x5
}
contradiction: ¬x2 generates both x6 and ¬x6
{
¬x1 ∨ x4,
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
x1 ∨ x5,
x1 ∨ x6,
¬x6 ∨ ¬x5
}
=
{
¬x2 ∨ x6 ∨ x4,
¬x4 ∨ ¬x2,
x2 ∨ x6,
x2 ∨ ¬x6 ∨ ¬x4,
x5,
x6,
¬x6 ∨ ¬x5
}
contradiction: x5, x6, ¬x6 ∨ ¬x5
set is unsatisfiable