Currently _is_preperiodic does not support dynamical systems defined on subschemes. This ticket aims to add support for morphisms of projective space defined over a subscheme.

CC: @bhutz

Component: dynamics

Keywords: gsoc2021

Author: Alexander Galarraga

Branch/Commit: u/gh-EnderWannabe/is_preperiodic @ faf2b23

Reviewer: Ben Hutz

Issue created by migration from https://trac.sagemath.org/ticket/32338