“…To overcome these difficulties, "cutting" the non-coercivity term and using the technique of approximation, a pseudomonotone and coercive differential operator on W 1,p 0 (Ω) can be applied to establish a priori estimates on approximating solutions. As a result, existence of solutions, or entropy solutions, can be obtained by taking limitation for f ∈ L m (Ω), m ≥ 1, and b > 0 due to the almost everywhere convergence of gradients of the approximating solutions, see, e.g., [4,6,[9][10][11]15] (see also [1,2,7,12,13,16] for b = 0). However, there is little literature that considers regularities for entropy solutions of obstacle problems governed by (1) and functions (f , ψ, g) with f ∈ L 1 (Ω), except [19], in which the authors considered the obstacle problem (7) with b = 0 and L 1 -data.…”