Claudius Bouillier designed l’ As (The Ace) as a simple, easy to use 3 speed derailleur for everyman. It includes a number of features that made their way onto the later, and much greater Le Cyclo. It is driven laterally by a peg running in a kind-of helical groove in the main axle, the pivot of the pulley cage is concentric with the guide pulley and it has that signature look.
However it also had a clever, lever-less design. You back pedaled briefly to get it to make a gear change. The change sequence was 3rd to 1st, 1st to 2nd and then 2nd to 3rd. The mechanism used a cunning sequential, spring-loaded, locking device.
When this derailleur finally went into production (by Brunet & Cie of Grand-Croix, 20 km North East of St Étienne) it was simplified to be a two speed system. The production L’As was regarded as a touring model which could handle a 10 tooth difference between the two sprockets.