generalize o.term = s
L : Language
ξ : Type u_1
n k : ℕ
o : Operator L k
v : Fin k → Semiterm L ξ (n + 1)
⊢ ((Rew.substs v) (Rew.emb o.term)).bv = o.term.bv.biUnion fun i => (v i).bv
L : Language
ξ : Type u_1
n k : ℕ
o : Operator L k
v : Fin k → Semiterm L ξ (n + 1)
s : Semiterm L Empty k
⊢ ((Rew.substs v) (Rew.emb s)).bv = s.bv.biUnion fun i => (v i).bv