Application( Cont. Example(Graphs) Let C=R) where R is a binary relation. We can characterize undirected irreflexive graphs with O VXR(x, x), oxvy(R(x,y)→R(y,x)Application(Cont.) . Example (Graphs) . . Let L = {R} where R is a binary relation. We can characterize undirected irreflexive graphs with 1. ∀x¬R(x, x), 2. ∀x∀y(R(x, y) → R(y, x)). Yi Li (Fudan University) Discrete Mathematics June 9, 2013 6 / 15