In any case, should the algebraical
nature of stretch change, e.
To solve the system of equations (9) we use strictly algebraical
We therefore aim to describe the medium pervading space, by means of the algebraical
sum of two energy-momentum tensors
Accordingly, when some combinations of an unknown and numbers represent a simple algebraical
problem, for example, of a sum or a difference, the relative position of the unknown in the equation determines the difficulty of the problem.
As in the other chapters, Kurdas employs simple algebraical
expressions and diagrams to crystallize complicated theorems.
Besides these three main considerations, the theory of gravitational waves is directly linked to the algebraical
classification of spaces given by Petrov  (Petrov classification), according to which three kinds for spaces (gravitational fields) exist.