\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]{}