feat(data/fin): help `simp` reduce expressions containing `fin.succ_above` (#7308)
feat(data/fin): help `simp` reduce expressions containing `fin.succ_above` (#7308)

With these `simp` lemmas, in combination with #6897, `simp; ring` can almost automatically compute the determinant of matrices like `![![a, b], ![c, d]]`.



Co-authored-by: Anne Baanen <839f20e486a83a313cf46ca4094e2de98129fc5d@users.noreply.github.com>

leanprover-community/mathlib,leanprover-community/mathlib