  The shape of an electronic droplet in the quantum Hall effect is sensitive to
gradients of the magnetic field, even if they are placed outside the droplet.
Magnetic impurities cause a fingering instability of the edge of the droplet,
similar to the Saffman-Taylor fingering instability of an interface between two
immiscible phases. We discuss the fingering instability and some algebraic
aspects of the electronic states in a strong nonuniform field.
