Goal:
    A : Type  n : nat  hd : A  tl : list A  H : S n < #|hd :: tl|
  ============================
   (S n ≤ #|tl|)


DEBUG:Going to execute:
match H with
           | H' => fail 2
           | _ => unify X Y; clear H' || clear H
           end
Level 4: Backtrace:

In environment
A : Type
n : nat
hd : A
tl : list A
H : S n < #|hd :: tl|
Unable to unify "nat" with "list A".
Level 4: Backtrace:

In environment
A : Type
n : nat
hd : A
tl : list A
H : S n < #|hd :: tl|
Unable to unify "nat" with "list A".
Level 4: Backtrace:

In environment
A : Type
n : nat
hd : A
tl : list A
H : S n < #|hd :: tl|
Unable to unify "nat" with "list A".
Level 4: Backtrace:

In environment
A : Type
n : nat
hd : A
tl : list A
H : S n < #|hd :: tl|
Unable to unify "nat" with "list A".
Level 3: Backtrace:

In environment
A : Type
n : nat
hd : A
tl : list A
H : S n < #|hd :: tl|
Unable to unify "nat" with "list A".