In a constrained triangulation, the information about constrained edges is stored in the faces of the triangulation. The base face of a constrained triangulation has to be a model of the concept ConstrainedTriangulationFaceBase_2 which refines the concept TriangulationFaceBase_2 providing functionalities to deal with constraints.

 
returns true if the edge between f and its neighbor
f.neighbor(i) is constrained. Precondition: $$0 i 2. 
advanced 

 
sets the edge between f and its neighbor f.neighbor(i) as a constrained or unconstrained edge according to b.  

 
sets the status (constrained or unconstrained) of the three edges of f.  

 Changes the orientation of f by exchanging vertex(0) with vertex(1) and neighbor(0) with neighbor(1) and the corresponding constrained status. 

 performs a counterclockwise permutation of the vertices, neighbors and constrained status of f. 

 performs a clockwise permutation of the vertices and neighbors and constrained status of f. 
advanced 
CGAL::Constrained_triangulation_face_base_2<Traits>