 An immediate obstacle to reading PM is the unfamiliar use of dots for punctuation, instead of the more common parentheses and brackets. The system is precise, and can be learned with just a little practice. The use of dots for punctuation is not unique to PM. Originating with Peano, it was later used in works by Alonzo Church, W.V.O. Quine, and others, but it has now largely disappeared. Alan Turing made a study of the use of dots from a computational point of view in 1942, presumably in his spare time after a day’s work at Bletchley Park breaking the codes of the Enigma Machine. Turing suggests that the use of juxtaposition to indicate conjunction is similar to the use of juxtaposition arithmetic to indicate multiplication: