Function break_parent_func_cycle 

pub fn break_parent_func_cycle<F>(
    parent_func: F,
) -> impl Fn(Vertex) -> Result<Vec<Vertex>>
where
    F: Fn(Vertex) -> Result<Vec<Vertex>>,

Pre-process a parent function that might have cycles. Return a new parent function that won’t have cycles.

This function is not fast. Only use it on small graphs.