One-Factorization of Complete Graphs of Even Order Combinatorics Closed Sets of a Closure Operator Form a Complete Lattice Combinatorics Closure Implies Distributivity Set Theory Bases Are Exactly Independent Spanning Sets Discrete Mathematics Recursive Atom Ordering Implies CL-Shellability Combinatorics Edmonds-Karp Distance Monotonicity Lemma Combinatorics Finite-Support Iteration Theorem for Ccc Forcing Set Theory Birkhoff Von Neumann Theorem Combinatorics Discrete Mathematics Area Combinatorics Subarea