* //
qed.
-(* Inversion with nsucc *****************************************************)
+(* Inversions with nsucc ****************************************************)
(*** nat_split *)
-lemma nat_split (n): ∨∨ 𝟎 = n | n = ↑↓n.
+lemma nat_split_zero_pos (n): ∨∨ 𝟎 = n | n = ↑↓n.
#n @(nat_ind_succ … n) -n
/2 width=1 by or_introl, or_intror/
qed-.