 If e.g. I have a method for looking at integers that satisfy the equation \(x^2 + y^2 = z^2\), then the formula \(x^{n} + y^n = z^{n}\) may stimulate me. I may let a formula stimulate me. Thus I shall say, Here there is a stimulus—but not a question. Mathematical problems are always such stimuli. (WVC 144, Jan. 1, 1931)