Goal:
  
  b : Byte.byte
  x : string
  IHx : forall y z : t,
        compare x y = Lt -> compare y z = Lt -> compare x z = Lt
  ============================
   (forall z : t,
    Gt = Lt ->
    match z with
    | ""%bs => Eq
    | String _ _ => Lt
    end = Lt ->
    match z with
    | ""%bs => Gt
    | String y ys =>
        match ByteCompare.compare b y with
        | Eq => compare x ys
        | Lt => Lt
        | Gt => Gt
        end
    end = Lt)


DEBUG:Going to execute:
congruence
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

Tactic failure: congruence failed.