Abstract: We investigate the operator in the plane with
an attractive singular interaction supported by a loop, and
show that in the strong-coupling limit the negative eigenvalues
converge to those of the Schroedinger operator on the loop
with the usual curvature-induced potential. We also derive an
estimate on the number of eigenvalues which has the correct
semiclassical behaviour. For more details see P. Exner and
K. Yoshitomi, math-ph/0103029.