"Logical machines 1870 – Stanley Jevons' "logical abacus" and "logical machine"": The technical problem was to reduce Boolean equations when presented in a form similar to what is now known as Karnaugh maps. Jevons (1880) describes first a simple "abacus" of "slips of wood furnished with pins, contrived so that any part or class of the combinations can be picked out mechanically ... More recently, however, I have reduced the system to a completely mechanical form, and have thus embodied the whole of the indirect process of inference in what may be called a "Logical Machine"" His machine came equipped with "certain moveable wooden rods" and "at the foot are 21 keys like those of a piano [etc ...". With this machine he could analyze a "syllogism or any other simple logical argument".