⊦ ns ⊆ ns0 ↔ (∀ n. n ∈ ns → n ∈ ns0)
ri.lebs ⊆ ns ⊦ (ri \ ks).lebs ⊆ ri.lebs, ∀ n. n ∈ (ri \ ks).lebs → n ∈ ns
Used terms: ns, (ri \ ks).lebs