“…Our goal is to construct a linear operator E h : (1.5) where Π h : C(Ω) −→ V h is the Lagrange nodal interpolation operator, and the positive constants C and C only depend on the shape regularity of T h and k. Moreover, the operator E h maps V h ∩ H 1 0 (Ω) into H 2 (Ω) ∩ H 1 0 (Ω). Enriching operators that satisfy (1.4) and (1.5) are useful for a priori and a posteriori error analyses for fourth order elliptic problems [8,17,6,7,9], and they also play an important role in fast solvers for fourth order problems [4,5,10]. A recent application to Hamilton-Jacobi-Bellman equations can be found in [21].…”