quoracle\quorum_system.py

"""
Original code available at: https://github.com/mwhittaker/quoracle/blob/d83a811a905a51fc13ebc00ddac036d559463380/quoracle/quorum_system.py#L276
"""

def _f_resilient_quorums(self,
                         f: int,
                         xs: List[T],
                         e: Expr) -> Iterator[Set[T]]:
    """
    Consider a set X of elements in xs. We say X is f-resilient if, despite
    removing an arbitrary set of f elements from X, X is a quorum in e.
    _f_resilient_quorums returns the set of all f-resilient quorums.
    """
    assert f >= 1

    def helper(s: Set[T], i: int) -> Iterator[Set[T]]:
        if all(e.is_quorum(s - set(failure))
               for failure in itertools.combinations(s, min(f, len(s)))):
            yield set(s)
            return

        for j in range(i, len(xs)):
            s.add(xs[j])
            yield from helper(s, j + 1)
            s.remove(xs[j])

    return helper(set(), 0)