StackSortable
1 when p avoids the pattern 231, 0 otherwise — exactly the stack-sortable permutations.
StackSortable(p)
Details
- Defined over `Permutation` as an expression in `_x`, evaluated by compute-engine — the definition IS the implementation.
- Takes a `Permutation`, and also a bare list of integers: this reading compares entries with each other rather than with their positions, so it stands on any sequence.