Fig. 27

Example of oriented mesh. An arrow represents the orientation of each edge and each face. The oriented face \(f_1=[v_1,v_2,v_3]\) is the equivalence class of \((v_1,v_2,v_3)\) with respect to relation (130), the oriented face \(f_2\) is the equivalence class of \((v_2,v_4,v_3)\). The oriented edge \(e_1\) is the equivalence class of \((v_1,v_2)\), etc.