## Kernel::CompareDihedralAngle_3

A model for this must provide:

Comparison_result fo.operator() ( K::Point_3 a1, K::Point_3 b1, K::Point_3 c1, K::Point_3 d1, K::FT cosine)
compares the dihedral angles 1 and 2, where 1 is the dihedral angle, in [0, π], of the tetrahedron (a1, b1, c1, d1) at the edge (a1, b1), and 2 is the angle in [0, π] such that cos(2) = cosine. The result is the same as operator()(b1-a1, c1-a1, d1-a1, cosine).
 Precondition: a1, b1, c1 are not collinear, and a1, b1, d1 are not collinear.

Comparison_result
 fo.operator() ( K::Point_3 a1, K::Point_3 b1, K::Point_3 c1, K::Point_3 d1, K::Point_3 a2, K::Point_3 b2, K::Point_3 c2, K::Point_3 d2)
compares the dihedral angles 1 and 2, where i is the dihedral angle in the tetrahedron (ai, bi, ci, di) at the edge (ai, bi). These two angles are computed in [0, π]. The result is the same as operator()(b1-a1, c1-a1, d1-a1, b2-a2, c2-a2, d2-a2).
 Precondition: For i ∈ {1,2}, ai, bi, ci are not collinear, and ai, bi, di are not collinear.

Comparison_result fo.operator() ( K::Vector_3 u1, K::Vector_3 v1, K::Vector_3 w1, K::FT cosine)
compares the dihedral angles 1 and 2, where 1 is the dihedral angle, in [0, π], between the vectorial planes defined by (u1, v1) and (u1, w1), and 2 is the angle in [0, π] such that cos(2) = cosine.
 Precondition: u1 and v1 are not collinear, and u1 and w1 are not collinear.

Comparison_result
 fo.operator() ( K::Vector_3 u1, K::Vector_3 v1, K::Vector_3 w1, K::Vector_3 u2, K::Vector_3 v2, K::Vector_3 w2)
compares the dihedral angles 1 and 2, where i is the dihedral angle between the vectorial planes defined by (ui, vi) and (ui, wi). These two angles are computed in [0, π].
 Precondition: For i ∈ {1,2}, ui and vi are not collinear, and ui and wi are not collinear.