have := mem_russellSet_iff.mp h'
case pos
V : Type u_1
inst✝ : Zermelo V
x✝ y z x : V
h : russellSet x ∈ x
h' : russellSet x ∈ russellSet x
⊢ False
case pos
V : Type u_1
inst✝ : Zermelo V
x✝ y z x : V
h : russellSet x ∈ x
h' : russellSet x ∈ russellSet x
this : russellSet x ∈ x ∧ ¬russellSet x ∈ russellSet x
⊢ False