A Lyapunov inequality for a second order nonlinear differential equation

This paper presents a Lyapunov-type inequality for the second order nonlinear equation (r(x)y′)′+p(x)f(y(x))=0(r(x)y′)′+p(x)f(y(x))=0, with r(x),p(x)>0r(x),p(x)>0 and f(y)f(y) odd and positive for y>0y>0. It also compares it with similar results.