He distinguished levels of logical reasoning, and introduced the notion of metalogic. Vasiliev spent 1912-13 in Western Europe (mostly Germany) and published his salient works ``Logic and Metalogic'' and ``Imaginary (non-Aristotelian) logic''. Vasiliev constructed non-Aristotelian logic using the concepts, and even the manner of reasoning, common to Aristotelian logic. He was aware of the achievement in mathematical logic (and even carefully studied Ernst Schr*der 's works) but did not make an attempt to formalise ``imaginary'' logic.
Vasiliev
Ernst Schr*der