This paper deals with a class of nonsmooth interval-valued optimization
problems (NIVOPs) whose objective and constraints are interval-valued
functions (IVFs). For this, we propose a new concept of symmetric
invexity (S-invexity) for IVFs based on gH-symmetrically derivative, and
deduce a sufficient optimality condition for non-dominated solutions.
Furthermore, we establish appropriate duality theorems for Wolfe and
Mond-Weir type duals. Examples are also presented to illustrate
corresponding results.