Periodic boundary value problems for second order functional differential equations
The authors study the existence of solutions of periodic boundary value problems for the nonlinear second-order functional-differential equation \[ -x''(t)=f(t,x(t),x_t), \quad t\in [0,2\pi], \qquad x(0)=x(2\pi), \quad x'(0)=x'(2\pi). \tag{1} \] By establishing some comparison results and using monotone iterative technique two theorems on the existence of maximal and minimal solutions of (1) are obtained.
scientific article; zbMATH DE number 2174212