“…To our knowledge, no sufficiently detailed analysis for non-smooth Γ was carried out so far. Being based on the general machinery for problems with corners [5,8,16] one might expect that if Γ is piecewise smooth with non-zero angles, then at least several lowest eigenvalues behave as E n (H α ) ≃ −µ n α 2 as α → +∞, where µ n ∈ ( 1 4 , 1) are spectral quantities associated with some model operators (so-called star leaky graphs) whose exact values are not known: we refer to [7,9,11,18,21] for a number of estimates.…”