Colinear
Let \(G\) be an incidence geometry . We call two points \( A,B \in G \) colinear if there exists a line \( l \) containing both \(A\) and \(B\). We call \(A\) and \(B\) non-colinear otherwise.
(sidenote: By definition of \(G\), any two points are colinear by axiom (1), so that non-colinear points must occur in triples. Indeed axiom (3) for incidence geometry ensures the existence of non-colinear points. )