+ ∧∧ 𝗱n = l & p ϵ ▵ɱ.t.
+#t #p #l #n * #q * #r #Hr
+<list_append_lcons_sn #H0 destruct -H0
+/4 width=4 by ex2_intro, ex_intro, conj/
+qed-.
+
+lemma prototerm_in_root_inv_lcons_mark:
+ ∀t,p,l. l◗p ϵ ▵ɱ.t →
+ ∧∧ 𝗺 = l & p ϵ ▵t.
+#t #p #l * #q * #r #Hr
+<list_append_lcons_sn #H0 destruct