$\newcommand {\N }{\mathbb {N}}$$\newcommand {\Z }{\mathbb {Z}}$$\newcommand {\Q }{\mathbb {Q}}$$\newcommand {\R }{\mathbb {R}}$$\newcommand {\E }{\mathbb {E}}$$\newcommand {\id }{\operatorname {id}}$$\newcommand {\Isom }{\operatorname {Isom}}$$\newcommand {\defeq }{\mathrel {\mathop {:}}=}$$\newcommand {\eqdef }{=\mathrel {\mathop {:}}}$$\newcommand {\abs }[1]{\lvert #1 \rvert }$$\newcommand {\floor }[1]{\left \lfloor #1 \right \rfloor }$$\newcommand {\ceil }[1]{\left \lceil #1 \right \rceil }$$\newcommand {\seg }[1]{\overline {#1}}$$\newcommand {\strahl }[1]{\overrightarrow {#1}}$$\newcommand {\ang }{\sphericalangle }$$\newcommand {\gang }{\angle }$$\newcommand {\paritaet }{\operatorname {par}}$$\newcommand {\drehw }{\operatorname {ang}}$$\newcommand {\vektor }[1]{\underline {#1}}$$\renewcommand {\vec }{\operatorname {vec}}$$\newcommand {\protect }[1]{}$