Unconditionality of orthogonal spline systems in $H^1$
  We give a simple geometric characterization of knot sequences for which the corresponding orthonormal spline system of arbitrary order $k$ is an unconditional basis in the atomic Hardy space $H^1[0,1]$. 
Gegham Gevorkyan and Anna Kamont and Karen Keryan and Markus   Passenbrunner
math.FA