Lean4
/-- The push forward of a complete sublattice under a complete lattice hom is a complete
sublattice. -/
@[simps]
def map (L : CompleteSublattice α) : CompleteSublattice β
where
carrier := f '' L
supClosed' := L.supClosed.image f
infClosed' := L.infClosed.image f
sSupClosed' := fun s hs ↦ by
obtain ⟨t, ht, rfl⟩ := subset_image_iff.mp hs
rw [← map_sSup]
exact mem_image_of_mem f (sSupClosed ht)
sInfClosed' := fun s hs ↦ by
obtain ⟨t, ht, rfl⟩ := subset_image_iff.mp hs
rw [← map_sInf]
exact mem_image_of_mem f (sInfClosed ht)