Tri and Poly Mesh relationship

When creating/mutating mesh:

• PolyMesh is less restrictive than TriMesh
• TriMesh is subtype of PolyMesh
• TriMesh is more specialized
• Related methods
  • add_face

When dealing with mesh:

• PolyMesh is subtype of TriMesh
• PolyMesh is more restrictive than TriMesh
• Related methods
  • vertices_of_face
  • faces_around_face
  • edges_around_face
  • flip_edge

Methods that are not effected by this:

• remove_face
• collapse_edge