Comment (by Roland Haas):

@helvi witek @Miguel Zilhão you are both listed as Lean maintainers in the README file, and I have assigned the ticket to the first one listed. If you would like to change that assignment you should be able to do so via the “Edit” button of the ticket.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2726/no-documentation-for-lean-codes