On learning in the limit and non-uniform (ε,δ)-learning

At least one coil partly surrounds a magnetic circuit consisting of a fixed yoke and a movable armature, the armature being constituted by a permanent magnet having pole faces adapted to carry pole-pieces which project on each side of the axis of magnetization. The electromagnet comprises a second permanent magnet interposed within the fixed yoke with a polarity such that the armature is urged towards the end or so-called rest position when the coil is not energized.