Simplification of "reciprocal word 3by2" (aka invert_pi1)

[Paul Zimmermann]

       Dear Paweł,

> I confirm this is a valid counter-example. Thank you very much.
> 
> If that is not a problem, are you able also to generate a case for t0 == d0?

I did not try, but you can using the method I described.

Best regards,
Paul