Goal:
    A : Type  d : A  n : nat  v : A  H : d = v
  ============================
   (None = None ∧ v = d)


DEBUG:Going to execute:
contradiction
Level 1: Backtrace:

 The relation and is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library
Level 0: Backtrace:

 The relation and is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library
Level 0: Backtrace:

 The relation and is not a declared symmetric relation. Maybe you need to require the Coq.Classes.RelationClasses library