"""Utilities for finding primal edges corresponding to dual edges."""
from typing import Any, cast

def get_edge_for_dual_edge(dual_edge: Any) -> tuple[int, int, None]:
    """Return the primal edge shared by both faces of the given dual edge."""
    edges: list[set[Any]] = []
    for e in (dual_edge[0] + dual_edge[1]):
        edge = set(e)
        if edge in edges:
            return cast(tuple[int, int, None], e)
        edges.append(edge)
    raise ValueError(f"Error finding edge for {dual_edge}")