fn optimize_orders(
    equivalences: &[Vec<MirScalarExpr>],
    available: &[Vec<Vec<MirScalarExpr>>],
    unique_keys: &[Vec<Vec<usize>>],
    input_mapper: &JoinInputMapper
) -> Vec<Vec<(Characteristics, Vec<MirScalarExpr>, usize)>>Notable traits for Vec<u8, A>impl<A> Write for Vec<u8, A> where
    A: Allocator