Let x0 of type ι be given.
Let x1 of type ι be given.
Assume H0: x1 ∈ x0.
Apply unknownprop_2ec38089a92dcd86a75a337a6e999322444786992f1b612acfe1d68011bad142 with
x0,
Sing x1.
Apply unknownprop_158329ee42f538f9f45353e081644457b58bf58b995713ab00dcbc514147ba46 with
x0,
x1.
The subproof is completed by applying H0.