feat(data/list): chain_iff_nth_le (#2354)
* feat(data/list): chain_iff_nth_le
* Update src/data/list/basic.lean
Co-Authored-By: Johan Commelin <johan@commelin.net>
* move
* fix
Co-authored-by: Scott Morrison <scott.morrison@anu.edu.au>
Co-authored-by: Johan Commelin <johan@commelin.net>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
