Abstract
We are concerned with the nonlinear second-order impulsive
periodic boundary value problem
u''(t)=f(t,u(t),u'(t)), t∈[0,T]∖{t1}, u(t1+)=u(t1−)+I(u(t1)), u'(t1+) =u' (t1−)+J(u(t1)), u(0)=u(T), u'(0)=u'(T), new criteria are established based on Schaefer's fixed-point theorem.