Ok, I need helps.
Greek philosopher is trapped in jail. There are 2 doors in the jail and 2 guards guarding the doors. 1 door leads to freedom, other to hell. The guard guarding the door to heaven never lies. The guard guarding the door to hell always lies. The philosophist can go out from either of those doors and he can ask 1 question from those guards. He asks "Are you guarding the door to heaven?". The guards answers either "yes" or "no". Now, how can the philospher be sure which guard is guarding which door and get out safely?