* https://wiki.selfhtml.org/wiki/PHP/Tutorials/Einstieg/Grundlagen#Einfache_Typen_und_ihre_Literale
  * https://www.php.net/manual/de/language.types.integer.php
  * https://www.php.net/manual/de/language.types.float.php
  * https://www.php.net/manual/de/language.operators.arithmetic.php
  * https://www.php.net/manual/de/ref.math.php