Goal:
    x : byte
  ============================
   (let H := CoreTactics.block in let H0 := CoreTactics.block in x = x)


DEBUG:Going to execute:
CoreTactics.intros_until_block
Level 2: Backtrace:

Tactic failure (level 1).
Level 1: Backtrace:

Tactic failure.
Level 0: Backtrace:

Tactic failure.