parent of plethysm

<div id="comment:0"></div>



Depends on #34470

CC:  @zabrocki

Component: **combinatorics**

Keywords: **conversion**

Author: **Martin Rubey**

Branch/Commit: **[`0dcc0aa`](https://github.com/sagemath/sagetrac-mirror/commit/0dcc0aa5532cb83322880e3dbc6b2a5019e3463f)**

Reviewer: **Travis Scrimshaw**

_Issue created by migration from https://trac.sagemath.org/ticket/27652_

