“…. , D k ), called a metric-affine almost multi-product manifold, appears in studies of the curvature and Einstein equations on multiply twisted and multiply warped products, see [10,11,12,13,16,20,35,36], in the theory of webs composed of different foliations, see [1], and Dupin hypersurfaces, (which have a constant number of different principal curvatures), see [9,25]. We define the mixed scalar curvature of (M, g, ∇; D 1 , .…”