Lean4
/-- The inf of Boolean subalgebras is their intersection. -/
instance instInfSet : InfSet (BooleanSubalgebra α) where
sInf
S :=
{ carrier := ⋂ L ∈ S, L
bot_mem' := mem_iInter₂.2 fun _ _ ↦ bot_mem
compl_mem' := fun ha ↦ mem_iInter₂.2 fun L hL ↦ compl_mem <| mem_iInter₂.1 ha L hL
supClosed' :=
supClosed_sInter <| forall_mem_range.2 fun L ↦ supClosed_sInter <| forall_mem_range.2 fun _ ↦ L.supClosed
infClosed' :=
infClosed_sInter <| forall_mem_range.2 fun L ↦ infClosed_sInter <| forall_mem_range.2 fun _ ↦ L.infClosed }