Hint Resolve Apart_imp_Sym.

(* Specifications: *)
Theorem sym_DiPt : forall x y : Point, DiPt x y -> DiPt y x.
Theorem sym_DiLn : forall x y : Line, DiLn x y -> DiLn y x.
Theorem sym_ConLn : forall x y : Line, ConLn x y -> ConLn y x.
Hint Immediate sym_DiPt sym_DiLn sym_ConLn.
Theorem Neg_apart_equiv :
forall (U : Set) (R : Relation U),
Apartness U R -> Equivalence U (Negation U R).