Using the standard (type class based) transitivity tactic for more contr...

...olable proof terms. As discussed in #454.
It's not an error message; it's feedback on what the command is doing.  It's saying "you used to be at commit 4c... which had description 'Fix an off-by-one-error', and now you've moved to commit 6c... with description 'Fix a typo'".

You'll need to `push -f` because you `commit --amend`ed.