(** *** A proof via [pcofix]  To define the [paco] versions of [eqone] and [eqtwo], we apply the two constructors [paco1_2_0] and [paco1_2_1], respectively ("1" because we are dealing with unary predicates).  Again, the translation of the lemma and of its proof is almost trivial. *)
Definition eqtwo' t := paco1_2_1 eqone_gen eqtwo_gen bot1 bot1 t.
Hint Unfold eqone' eqtwo'.

Lemma eqone'_eins: eqone' eins.
Section safety.