Beste einseitige L1-Approximation mit Quasi-Funktionen
Let $I^2:=[-1,1] imes[-1,1]$ be the unit square and let $U$ be a subspace of $C(I^2)$. If $f$ is a continuous function, then $u^{ast}in U$ is said to be a {it best one--sided $L^1$--approximation to f in $U$ from above} if $u^{ast}geq f$ and $|f-u^{ast}|_1leq |f-u|$ for every $u in U$ with $ugeq f$. In this paper we consider the problem of characterization of such best approximants for the case where $U$ consists of all (quasi--)blending--functions of order $(m,1)$.