def test_literal():
assert literal_symbol(True) is True
assert literal_symbol(False) is False
assert literal_symbol(A) is A
assert literal_symbol(~A) is A
pytest.raises(ValueError, lambda: literal_symbol(A + B))
def test_literal():
assert literal_symbol(True) is True
assert literal_symbol(False) is False
assert literal_symbol(A) is A
assert literal_symbol(~A) is A
pytest.raises(ValueError, lambda: literal_symbol(A + B))
def find_unit_clause(clauses, model):
"""
A unit clause has only 1 variable that is not bound in the model.
>>> from diofant import symbols
>>> from diofant.abc import A, B, D
>>> from diofant.logic.algorithms.dpll import find_unit_clause
>>> find_unit_clause([A | B | D, B | ~D, A | ~B], {A:True})
(B, False)
"""
for clause in clauses:
num_not_in_model = 0
for literal in disjuncts(clause):
sym = literal_symbol(literal)
if sym not in model:
num_not_in_model += 1
P, value = sym, not (literal.func is Not)
if num_not_in_model == 1:
return P, value
return None, None