Function expr::permutation_to_map_and_new_arity

pub fn permutation_to_map_and_new_arity(
    permutation: &[usize]
) -> (HashMap<usize, usize>, usize)

Takes a permutation represented as an array (where the ith column being j implies that column i in the original row corresponds to column j in the permuted row; see dataflow::render::Permutation) and converts it to a column map along with the arity of the permuted representation