On the other hand, "R"T "R" is a relation on "B" × "B" which "fails" to be universal because at least two oceans must be traversed to voyage from Europe to Oceania. 2) Visualization of relations leans on graph theory: For relations on a set (homogeneous relations), a directed graph illustrates a relation and a graph a symmetric relation. For heterogeneous relations a hypergraph has edges possibly with more than two nodes, and can be illustrated by a bipartite graph. Just as the clique is integral to relations on a set, so bicliques are used to describe heterogeneous relations; indeed, they are the "concepts" that generate a lattice associated with a relation. 3) Hyperbolic orthogonality: Time and space are different categories, and temporal properties are separate from spatial properties. The idea of "simultaneous events" is simple in absolute time and space since each time "t" determines a simultaneous hyperplane in that cosmology. Herman Minkowski changed that when he articulated the notion of "relative simultaneity", which exists when spatial events are "normal" to a time characterized by a velocity. He used an indefinite inner product, and specified that a time vector is normal to a space vector when that product is zero. The indefinite inner product in a composition algebra is given by As a relation between some temporal events and some spatial events, hyperbolic orthogonality (as found in split-complex numbers) is a heterogeneous relation. 4) A geometric configuration can be considered a relation between its points and its lines. The relation is expressed as incidence. Finite and infinite projective and affine planes are included. Jakob Steiner pioneered the cataloguing of configurations with the Steiner systems S("t,k,n") which have an n-element set "S" and a set of k-element subsets called blocks, such that a subset with "t" elements lies in just one block. These incidence structures have been generalized with block designs. The incidence matrix used in these geometrical contexts corresponds to the logical matrix used generally with binary relations. Heterogeneous relations have been described through their induced concept lattices: A concept "C" ⊂ "R" satisfies two properties: (1) The logical matrix of "C" is the outer product of logical vectors  For a given relation "R": "X" → "Y", the set of concepts, enlarged by their joins and meets, forms an "induced lattice of concepts", with inclusion formula_5 forming a preorder.