O. Davydov, Locally linearly independent basis for $C^1$
bivariate splines of degree $q\ge 5$, in "Mathematical Methods for Curves
and Surfaces II" (M.Daehlen, T.Lyche, L.L.Schumaker, Eds.), pp. 71-78,
Vanderbilt University Press, 1998.

Abstract: We construct a locally linearly independent basis for
the space $\S^1_q(\Delta)q$ ($q\ge5$). Bases with this property were available
only for some subspaces of smooth bivariate splines.