GENERIC INTERFACE Vector4Extras(VRep);
(*
  Vector operations specific to 4-dimensional vector spaces: *)

PROCEDURE Det(READONLY a, b, c, d: VRep.T): LONGREAL;
  (*
    Returns the determinant of the matrix whose rows are "a", "b", "c". *)

PROCEDURE Cross(READONLY a, b, c: VRep.T): VRep.T;
  (*
    The cross product of "a", "b", "c" --- that is, a vector
    "r" orthogonal to all three, such that "Det(a, b, c, x) = Dot(r, x)"
    for any vector "x". *)
    
END Vector4Extras.