Goal:
  
  P : E.t -> Prop
  s : t
  P_dec : forall x : E.t, {P x} + {~ P x}
  P_Proper : Proper (E.eq ==> impl) P
  H : ~ List.Exists P (elements s)
  H' : Exists P s
  ============================
   False


DEBUG:Going to execute:
apply H, Exists_alt_iff, H'

COQC theories/MCPred.v