One item, everything we know about it, and everything it is connected to.
Words we use: Mystery A question nobody has answered yet. Clue from people Something people wrote down or told long ago: a chronicle, a diary, a story, a carving. Clue from nature Something nature recorded by itself: tree rings, ice, rock layers, or the leftovers of an exploded star. Hunch Our guess that a clue from people and a clue from nature are about the same event. Book or paper Where we read it, so anyone can check our work. Step Something we did, in the order we did it.
Remnant RX J1713.7-3946 proposed; two nova candidates rated equally likely. Undecidable at present. Parked.