Now, Watson," said he, "we have picked up two clues this morning. One is the bicycle with the Palmer tyre, and we see what that has led to. The other is the bicycle with the patched Dunlop. Before we start to investigate that, let us try to realize what we do know, so as to make the most of it, and to separate the essential from the accidental.
Arthur Conan Doyle, The Adventure of the Priory School
logic, mystery