Definition:Hilbert 23/21

Hilbert $23$: Problem $21$

Existence of Linear Differential Equation with prescribed Monodromic Group

Proof of the existence of linear differential equations having a prescribed monodromic group.

Historical Note

The Hilbert 23 were delivered by David Hilbert in a famous address at Paris in $1900$.

He considered them to be the oustanding challenges to mathematicians in the future.

There was originally going to be a $24$th problem, on a criterion for simplicity and general methods in proof theory, but Hilbert decided not to include it, as it was (like numbers $4$, $6$, $16$ and $23$) too vague to ever be described as "solved".