I have the following problem with the commands "Infinitesimals" and "InvariantSolutions". After using them to a system of firsst-order PDE's, the following message appears:

 

 Error, (in table["k"]) expected a request of prolongation w.r.t one of 2 independent variables; received a request w.r.t the (inexistent) 4th one

Does anybody know, what this message means ? I am a beginner with the commands "Infinitesimals" and "InvariantSolutions"...

I would like to ask, whether MAPLE can compute expressions written in covariant notation, like these ones (I have written it in LATEX): $u^{\mu \alpha}_{\nu} u_{\mu} u^{\nu} v_{\alpha}$, (where $\mu, \nu, \alpha = 0,...3$), i.e. whether we can compute the summation (like in these above examples), contraction, substitute ansatzes for $u$, compute derivatives of this above expressions, etc. I looked for any information in documentation, but I did not found anything. I checked,...