Theorem: SetTheory.inter_assoc (SetTheory/Basic.lean)

State before:
V : Type u_1
inst✝ : Zermelo V
x y z : V
⊢ x ∩ y ∩ z = x ∩ (y ∩ z)
Tactic:
ext
State after:
case h
V : Type u_1
inst✝ : Zermelo V
x y z z✝ : V
⊢ z✝ ∈ x ∩ y ∩ z ↔ z✝ ∈ x ∩ (y ∩ z)

State before:
case h
V : Type u_1
inst✝ : Zermelo V
x y z z✝ : V
⊢ z✝ ∈ x ∩ y ∩ z ↔ z✝ ∈ x ∩ (y ∩ z)
Tactic:
aesop
State after:
no goals