Canonical gauge-invariant variables for scalar perturbations in synchronous coordinates

Under an appropriate change of the perturbation variable Lifshitz-Khalatnikov propagation equations for the scalar perturbation reduce to d'Alembert equation. The change of variables is based on the Darboux transform.Comment: LaTeX, 9 page

Symbolic Tensor Calculus -- Functional and Dynamic Approach

In this paper, we briefly discuss the dynamic and functional approach to computer symbolic tensor analysis. The ccgrg package for Wolfram Language/Mathematica is used to illustrate this approach. Some examples of applications are attached