... as the not-Ys in the one premiss may be different from those in the other, no conclusion can be drawn. The mathematical condition in question, therefore, the irreducibilityof the final equation ... Propositions admit of negative conver-sion, or, as it is also termed, conversion by contraposition. The equations A and E, written in the forms(1 − y)x = 0,yx = 0,give on solution the respective ... expressed by equations, the elimina-tion of a common symbol between them leads to a third equation whichexpresses the conclusion, this conclusion being always the most generalpossible, whether...