Function could_come_within 

pub fn could_come_within<PA: Piece + Clone, PB: Piece + Clone>(
    a: Vec<PA>,
    b: Vec<PB>,
    reach: Scalar,
    handoff: Scalar,
    max_nodes: usize,
) -> GeopResult<bool>

Whether the set a is pieces of could come within reach of the set b is pieces of: least_distance’s search for a question that needs no least distance. A pair whose lower bound is definitely beyond reach is dropped before anything is asked of it, attaining a point being what costs on a trimmed face, and the first points attained within it end the search. So two parts a hair apart cost a few cuts, and two lying on each other one look. What the search cannot tell apart, at the handoff or at max_nodes pairs, could be within it.