Goal:
    x : byte  y : byte  Hcomp : Some x = Some y
  ============================
   (let H := CoreTactics.block in x = y)


DEBUG:Going to execute:
CoreTactics.block_goal
Level 4: evaluation returns
idtac of type tacvalue

Level 2: evaluation returns
idtac of type tacvalue

Level 1: evaluation returns
idtac of type tacvalue