A Note on Semiconcave Function

This article gives a simple proof of an equivalent proposition on semiconcave function (see L.C. Evans (1998). Partial Differential Equations. American Mathematical Society; p. 130]). The proof of sufficiency of the proposition can be easily obtained. We prove its necessity by three steps: First, we prove that the equivalent proposition holds for discrete points <artwork name="GAPA31045ei1">; Secondly, we obtain continuity of semiconcave function; Finally, by using the fact that the sequences λ_m ^k are dense in the interval (0, 1), we prove that the equivalent proposition holds for each λ ∈ (0, 1).