Nebesky, L.

graph axiom function interval function interval system lemma graph g proof signpost signpost system vertice characterization block theorem nebesk operation step system mulder cycle ternary process vertex geodesic structure x ∈ f section leap operation guide induction z ∈ v result signpost systems proposition betweennes approach function f ym +n lemma c journal paper wheel geodesic structure satis fies axioms access operation article block graph corollary european combinatoric yi +m european journal press example obstruction distance ternary relation ym +1 distance function geodetic study cut-vertex nonempty ternary algebras length geodetic betweenness definition algebra j ≤ m x ∈ v contradiction property leap system induction hypothesis interval operator relation interval function i ¯ ¯ ¯ y ∈ v v ∈ v