The roots of many-valued logic lie in Aristotle's (4th century BC) discussion of future contingents and of tomorrow's famous sea battle. Similar concerns can be found in medieval philosophy, in Duns Scot, William of Ockham and Peter de Rivo (Louvain). However, one needs to wait until the turn of the twentieth century to see the first attempts at creating non-classical – mainly three-valued – systems. By the late 1890s, Hugh MacColl had presented his so-called "three-dimensional logic", Charles S. (1839–1914) was working on "trychotomic mathematics" and Nicolai A. Vasiliev was developing a system in which propositions can be "affirmative", "negative" or "indifferent".