apply not_iff_not.mp
α : Type
inst✝ : Hierarchical α
rtr✝ rtr₁ rtr : α
⊢ Acyclic rtr ↔ ∀ i ∈ rtr[Component.rcn], ¬i <[rtr] i
α : Type
inst✝ : Hierarchical α
rtr✝ rtr₁ rtr : α
⊢ ¬Acyclic rtr ↔ ¬∀ i ∈ rtr[Component.rcn], ¬i <[rtr] i