• shorten the code of area
• fix some SEEALSO cross-links inside the doc
• display some examples where there were TESTS only
• enhance some typing annotations
• do not use list as a variable
• more direct call to multinomial

CC: @tscrim @slel @kliem

Component: combinatorics

Author: Frédéric Chapoton

Branch/Commit: 7820aaa

Reviewer: Samuel Lelièvre

Issue created by migration from https://trac.sagemath.org/ticket/33095