English
If s is sup-independent and t ⊆ s and ⊥ ∈ s with f(i) ∈ s for i ∈ t, then s is closed under sup over i ∈ t.
Русский
Если s является SupIndep и t ⊆ s, а ⊥ ∈ s и все f(i) ∈ s, то sup по i ∈ t принадлежит s.
LaTeX
$$$\\text{SupIndep}(s) \\land t ⊆ s \\land ⊥ \\in s \\Rightarrow sSup_{i\\in t} f(i) \\in s.$$$
Lean4
theorem sSup_mem (hs : SupClosed s) (ht : t.Finite) (hbot : ⊥ ∈ s) (hts : t ⊆ s) : sSup t ∈ s :=
by
have := ht.to_subtype
rw [sSup_eq_iSup']
exact hs.iSup_mem hbot (by simpa)