We assume gravity in a d-dimensional manifold M and consider a splitting of the form M = Mp x Mq, with d = p + q. The most general two-block metric associated with Mp and Mq is used to derive the corresponding Einstein-Hilbert action S. We focus on the special case of two distinct conformal factors and ( for the metric in Mp and for the metric in Mq), and we write the action S in the form S = Sp+Sq, where Sp and Sq are actions associated with Mp and Mq, respectively. We show that a simplified action is obtained precisely when = -1. In this case, we find that under the duality transformation -1, the action Sp for the Mp-space or the action Sq for the Mq-space remain invariant, but not both. This result establishes an analogy between Farkas property in oriented matroid theory and duality in general relativity. Furthermore, we argue that our approach can be used in several physical scenarios such as 2t physics and cosmology.