“…It has been found out that local mesh refinement near corners and use of analytical formulas of asymptotic solution near corners produce better results for problems with corner singularities. Some of the popular techniques to overcome slow convergence are as follows: singular function method [19,35], singular complement method [2], dual singular function method [6,7,10,11], introduction of analytical constraints to finite element formulation [33], truncation of corners and introduction of Dirichlet-to-Neumann boundary conditions for domains with truncated corners [21], and other methods based on the similar ideas [26,34]. Also, various methods based solely on mesh refinement (without using asymptotic expansion of the solution) were developed (see, for example, [1,3,14,30,31]).…”