ruby-debug19 causes problems, don’t want to diagnose them, deleting.
WIP find_chains still, but tests pass.
New specification for find_chains.
New spec for Grid#groups_of: returns a Set.
Implementation thereof.
WIP find_chains.  That doesn’t work, need to rethink the structure.
Tweaking test for find_chains.
Added one more TODO.
Typographical changes in spec file.
Specs for convenience methods “name”.
Stupid typo in spec.
name implementation.
find_chains finally works!  But it’s a bloody mess now.
Output from Rspec on lib_spec.  It’s interesting ;-)
That’s the actual sample output.
Reinstated search over all groups, not only rows and columns.
Reinstated recursive call unconditionally.
Call depth counter now useless, removing.
Forgot to change that for the full group search.
Cleaned up messy debug printout’s.