'Iterate over the various forms of propagation to simplify the theory.
Examples
>>> from sympy.logic.algorithms.dpll2 import SATSolver
>>> l = SATSolver([{2, -3}, {1}, {3, -3}, {2, -2},
... {3, -2}], {1, 2, 3}, set())
>>> l.variable_set
[False, False, False, False]
>>> l.sentinels
{-3: {0, 2}, -2: {3, 4}, 2: {0, 3}, 3: {2, 4}}
>>> l._simplify()
>>> l.variable_set
[False, True, False, False]
>>> l.sentinels
{-3: {0, 2}, -2: {3, 4}, -1: set(), 2: {0, 3},
...3: {2, 4}}'

def _simplify(self):

    changed = True
    while changed:
        changed = False
        changed |= self._unit_prop()
        changed |= self._pure_literal()
