of deep binding. However, the 2P state becomes bound into the square well near $\lambda b^2=\pi^2$, earlier than the 2S for which this occurs near $\lambda b^2=9 \pi^2/4$. This explains the observed crossing.

In the harmonic oscillator case, there is a remarkable double crossing. The 2S drops by the phenomenon of rearrangement, and crosses the 2P level which is first almost unchanged. When the 2P level becomes bound by the square-well, it crosses again the 2S, which falls down for higher strength.

Note that those patterns do not contradict the general theorems on level ordering, which have been elaborated in particular for understanding the quarkonium spectra in potential models [@Quigg:1979vr; @Grosse:1997xu]. If the square well $\lambda v$ is considered as the large $n$ limit of $\lambda v_n(r)=-\lambda/ [1+ (r/b)^n]$, the Laplacian $\Delta v_n=(r v_n)''/r$ can be calculated explicitly, and is easily seen to be positive for small $r$ and negative for large $r$. Hence the theorem [@Quigg:1979vr; @Grosse:1997xu] stating that $E(2P)<E(2S)$ if $\Delta V>0$ and vice-versa cannot be applied here. In our case $V=-1/r+\lambda v$, with the Coulomb part having a vanishing Laplacian, or $V=r^2+\lambda v$, with $\Delta(r^2)>0$.

Figure \[fig:crossing\] clearly indicates that the rearrangement is much sharper for P-states 