DO NOT MERGE | Minimize inconsistent LaTeX failures

[WhatisRT]

Description

Since the same code sometimes works on my machine and sometimes doesn't, I'm using CI as a reproducible machine.

To reproduce locally, use nix-shell --command 'make ledger.docs'. The offending file is pretty much just PDF.lagda.

Ways to not make this fail:

• rename ff to f
• indent the last line of f3 (_ → true) by two more spaces
• remove pretty much anything