Abstract:  We present explicit formulae for calculating the Mordukhovich co-derivative to certain non-polyhedral sets. The necessity for said formulae are due to the fact that co-derivatives often appear within the optimality/stationarity conditions for certain equilibrium models with equilibrium constraints (EPECs). Such models have proven to be integral in the modelling of leader-follower type games, wherein non-polyhedrality as well as non-convexity of the feasible set is often inherent and unavoidable, regardless of the convexity and smoothness of the initial data, and thus leads to computational difficulties. A typical example of such an EPEC arises from the modelling of electricity spot markets, where the desire to model as realistically as possible requires the modeller to incorporate a quadratic term which takes into account transmission losses due to resistance.