Goal:
    A : Type  l : list A  hd : A  tl : list A
  ============================
   (Some hd = Some hd ∧ tl = tl)


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