Goal:
    x : V.t  s : VSet.t
  ============================
   (~ VSet.In x (VSet.remove x s))


DEBUG:Going to execute:
clear H
Level 1: Backtrace:

In environment
x : V.t
s : VSet.t
The term "VSet.t" has type "Type" while it is expected to have type 
"Prop" (universe inconsistency: Cannot enforce VSet.t.u0 <= Prop).