#hypnagogue  an agent that induces drowsiness or sleep
  subtype:  soporific  a drug that induces sleep
  supertype:  agent.causal_agent  a substance that exerts some force or effect
     supertype:  causal_agent__cause__causal_agency  any entity that causes events to happen
        supertype:  thing_playing_some_role  category to classify things according to roles/viewpoints; classification under this category is application-dependant
           supertype:  thing__something___T__t___3D_or_4D_thing_or_anything_else  any category (type or individual) is instance of this type; any type is also a subtype of this type

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