apply (CompleteLattice.I_isInf _).eq
X : Type
inst✝¹ : PartialOrder X
inst✝ : CompleteLattice X
x : X
⊢ Inf {x' | x ≤ x'} = x
X : Type
inst✝¹ : PartialOrder X
inst✝ : CompleteLattice X
x : X
⊢ isInf {x' | x ≤ x'} x