  The main purpose of this paper is to find conditions for Holder calmness of
the solution mapping, viewed as a function of the boundary data, of a
hemivariational inequality governed by the Navier-Stokes operator. To this end,
a more abstract model is studied first: a class of parametric equilibrium
problems defined by trifunctions. The presence of trifunctions allows the
extension of the monotonicity notions and of the duality principle in the
theory of equilibrium problems.
