“…Approximation of the Lipschitz extension problem by the sequence of functionals (8.4) as p → ∞ and taking a limit of the corresponding Euler-Lagrange equations were first proposed by Aronsson [5] and made completely rigorous, in case of the Euclidean norm, in [18]. Since then these ideas have been successfully employed in various settings and forms, e.g., in [13], [15], [19], [20], [39], [44], [47], [48], [50], [51], [54], [59], [60], and [64]. The facts about Sobolev spaces and functional analysis needed in order to prove the existence of p-harmonic functions by the direct method in calculus of variations can be found in many textbooks, see, e.g., [36] and [38].…”