Go backward to Example Go up to Top Go forward to Indirect Method for Universal Formulas |
We show
forall x in Z, y in Z: x+y = y+x.Take arbitrary x in Z,y in Z. We have
x+y = (definition of +) I(x +N y, x +N y) = (commutativity of +N) I(y +N x, y +N x) = (definition of +) y+x.
More typical version.