def find_unit_clause(clauses, model):
    """Find a unit clause has only 1 variable that is not bound in the model.

    Arguments are expected to be in integer representation.

    >>> find_unit_clause([{1, 2, 3}, {2, -3}, {1, -2}], {1: True})
    (2, False)

    """
    bound = set(model) | {-sym for sym in model}
    for clause in clauses:
        unbound = clause - bound
        if len(unbound) == 1:
            p = unbound.pop()
            if p < 0:
                return -p, False
            else:
                return p, True
    return None, None