Widths of weighted Sobolev classes with constraints f(a)=⋯=f(k−1)(a)=f(k)(b)=⋯=f(r−1)(b)=0f(a)=⋯=f(k−1)(a)=f(k)(b)=⋯=f(r−1)(b)=0 and the spectra of nonlinear differential equationsстатья