I read paper https://arxiv.org/ftp/arxiv/papers/1011/1011.3719.pdf . I do not understand figure 2. Such double phase space (x-p) can be also for a harmonic oscillator. But, at a harmonic oscillator we cannot have two ellipses (or a circle and an ellipse) which touch on some points, but have the same center. Maybe Greenberger thought something more general than Harmonic oscillator?