ABSTRACT
Φ(u1,u2) = 0, (23.1.1.4) where Φ(u, v) is an arbitrary function of two variables. With equation (23.1.1.4) solved for u1 or u2, we often specify the general solution in the form
uk = Ψ(u3-k), where k = 1, 2 and Ψ(u) is an arbitrary function of one variable.
