match fmla, h with
| fmla, Or.inl h => rw [Formula.subst_id]; exact Provable.hyp _ h
| _, Or.inr ⟨v, rfl⟩ => exact Provable.var v
axs : Statement → Prop
ax : Statement
H : axs ax
fmla : Formula
h : fmla ∈ ax.ctx.hyps ∨ ∃ v, fmla = VR.vhyp v
⊢ Provable axs ax.ctx (Formula.subst VR.expr fmla)
no goals