simp only [WellFormed, PWellFormed] at wf
I : Type u₀
C : IContainer' I
i : I
x✝ : M C i
m : Container.M (toContainer C)
wf : WellFormed i m
⊢ ∀ (x : B C (Container.M.destruct ↑{ val := m, property := wf }).fst),
    WellFormed (Next C (Container.M.destruct ↑{ val := m, property := wf }).fst x)
      (PSigma.snd (Container.M.destruct ↑{ val := m, property := wf }) x)
I : Type u₀
C : IContainer' I
i : I
x✝ : M C i
m : Container.M (toContainer C)
wf : ↑(pgfp (WellFormedF C)) ⊥ i m
⊢ ∀ (x : B C (Container.M.destruct ↑{ val := m, property := wf }).fst),
    WellFormed (Next C (Container.M.destruct ↑{ val := m, property := wf }).fst x)
      (PSigma.snd (Container.M.destruct ↑{ val := m, property := wf }) x)