Na podstawie prac:
Z. Ciesielski, Orthogonal projections onto spline spaces with arbitrary knots. Function spaces (Poznań, 1998), 133-140, Lecture Notes in Pure and Appl. Math., 213,
M.Passenbrunner, A.Shadrin, On almost everywhere convergence of orthogonal spline projections with arbitrary knots, preprint 2013, arXiv:1308.4824.