Goal:
  
  A : Type
  p : A → bool
  n : nat
  a : A
  l : list A
  IHl : ∀ n : nat, forallb p l → forallb p (skipn n l)
  ============================
   (p a && forallb p l → forallb p (skipn n l))


DEBUG:Going to execute:
<coq-core.plugins.cc::cc@0> $1