In some scientific areas such as polymer physics, one may consider a chain of points and links between consecutive points. If the points are sequentially numbered and located at positions , , , etc. bond vectors are defined by =-, =-, and =-, more generally. This is the case for kinematic chains or amino acids in a protein structure. In these cases, one is often interested in the planes defined by three consecutive points, and the dihedral angle between two consecutive such planes. If an orientation has been chosen for the whole chain, each pair of consecutive points defines a vector, and the sum of all these vectors is the vector pointining from the beginning to the end of the chain. If , and are three consecutive such vectors, one has a situation that is similar to the preceding case, except that the intersection of the planes is oriented. This allows defining a dihedral angle that belongs to the interval . This dihedral angle is defined by