  We study a pseudo-differential equation driven by the degenerate fractional
p-Laplacian, under Dirichlet type conditions in a smooth domain. First we show
that the solution set within the order interval given by a sub-supersolution
pair is nonempty, directed, and compact, hence endowed with extremal elements.
Then, we prove existence of a smallest positive, a biggest negative and a nodal
solution, combining variational methods with truncation techniques.
