consider a singly quantized vortex situated at the center of a superconducting disk of rather small radius $R$ comparable with the coherence length. In this case a constructive interference of quasiparticle waves reflected from the boundary is known to result in mesoscopic oscillations of energy levels[@MelnikovPrl2005]: $$\label{SpectrumDisc}
  \varepsilon(\mu)=-\omega\mu -\delta\sin(2k_FR-\pi \mu)\,,$$ where $\delta\sim \Delta_0\exp(-2R/\xi)$ and $|\varepsilon(\mu)|\ll\Delta_0$. The remarkable fact is that at low energies these levels can be combined into two groups corresponding to odd and even values of the integer index $\mu+1/2$. A spacing between the energy levels belonging to one group is $2\omega$ while the energy shift between the different groups is $2\delta|\cos(2k_F R)|$. Analogous shift of vortex core levels defined by the factor $\exp(-R/\xi)$ has been observed recently for a vortex-antivortex pair on a sphere with a finite radius $R$ in $p_x+ip_y$ superconductors[@Fertig]. Note that for a small superconducting disc with $R<R_c\sim (\xi/2)\ln (k_F\xi)$ we have $\delta\gg\omega$. Therefore the two groups of energy levels can be considered as continuous branches if the energy discreteness with the scale $\omega$ is neglected. In this approximation one can use a quasiclassical expression $\mu=-k_Fr\sin(\theta-\theta_p)$ and obtain the low energy branches in the form: $$\label{SpectrumDisc-q}
  \varepsilon_{1,2}
  =\omega k_Fr\sin(\theta-\theta_p)\pm\delta\cos(2k_F R)\,.$$ Thus, for low energies 