“…We require H r+3 ( ) regularity, mainly due to technical details involved in analysis of the quadrature error in Lemma 3.1. Such extra regularity assumption on the exact solution is essential for analysis of C 1 spline collocation methods that do not involve integrals, but require evaluation of functions at certain quadrature points [7,10,19]. The analysis in [1,2] for finite element Galerkin method with quadrature for a linear biharmonic problem, restricted to the C 1 cubic spline (r = 3) case, requires H r+5 ( ) regularity.…”