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Galois theory, named after Évariste Galois, provides a connection between field theory and group theory. Using Galois theory, certain problems in field theory can be reduced to group theory, which is, in some sense, simpler and better understood.

33 votes
Accepted

What justification can you give for the fact that "most ODEs do not have an explicit solution"?

If the ODE is linear --and the notion of «explicit» refers to Liouvillian solutions (towers of iterated quadrature and exponential of meromorphic functions)-- then its differential Galois group (Picar …
Loïc Teyssier's user avatar
11 votes

The holomorphic version of Galois theory

Say $a_n=1$. You can obtain this map as a section of the map $\sigma$ sending the $n$-tuple of the roots $(r_1,\ldots,r_n)$ to the coefficients of the polynomial using the symmetric polynomials, corre …
Loïc Teyssier's user avatar
5 votes
Accepted

Are all rational exactly solvable differential equations known?

I don't think a general answer to your question is known. I personnaly doubt that it could be positive. Partial decidable answer: if the variational linear differential system obtained along a give …
Loïc Teyssier's user avatar