# Un sous-syst\`eme d'un syst\`eme plat de dimension diff\'erentielle 2 est plat. A subsystem of a flat system of differential dimension 2 is flat

## TL;DR

The paper proves that subsystems of flat systems with differential dimension up to 2 are also flat, and stationary flat systems admit time-independent flat outputs, enhancing understanding of system flatness properties.

## Contribution

It establishes the flatness of subsystems with differential dimension at most 2 and demonstrates the existence of time-independent flat outputs for stationary flat systems.

## Key findings

- Subsystems of flat systems with differential dimension ≤ 2 are flat.
- Stationary flat systems have flat outputs independent of time.
- Provides theoretical insights into the structure of flat systems.

## Abstract

Un sous-syst\`eme de dimension diff\'erentielle au plus 2 d'une extension plate est plate. Si un tel syst\`eme plat est stationnaire, il admet des sorties plates ind\'ependantes du temps. A subsystem of a flat system of differential dimension at most 2 is flat. Furthermore, if such a flat system is stationary, we show that there exist flat utputs not depending on the time.