Semi-Fredholm problems on periodic solutions of functional-differential equations of neutral type (Q662446)

The problem of the existence of periodic solutions for linear systems of functional-differential equations of neutral type of the form \[ dx/dt \;(t)-A_1(t) \;dx/dt \;(t-h(t))+ A_2 (t)x(t)+A_3 (t)x(t-h(t))=f(t), \] is considered. By reduction to some associated operator equation, necessary and sufficient conditions are established under which the corresponding operator is Fredholm or semi-Fredholm.