happens(mine(a1),0).
happens(drain,1).
happens(drain,2).
happens(trade,3).
happens(mine(a2),4).
happens(mine(a0),5).
happens(down_to(a),6).
happens(mine(space_canary_corpse),7).
happens(mine(c0),8).
happens(down_to(c),9).
happens(down_to(f),10).
happens(up_to(c),11).
happens(up_to(a),12).
happens(down_to(c),13).
happens(down_to(f),14).