Chongo's method for Bobert to prove that he exists by visiting BillD is obviously completely fallacious, since what he describes for Bobert to do is exactly what BillD might expect a Bobert would do, and hence it does nothing to resolve the question of whether Bobert is a figment of his own imagination or a creation of BillD's.

It does not prove that Bobert thinks therefore Bobert is, rather than that BillD thinks Bobert thinks and therefor Bobert is. Of course there's the converse where Bobert thinks that BillD thinks so BillD exists only because Bobert thinks he thinks.

The problem of Chongo is of course more complex since obviously Chongo only thinks he thinks, so he can only think he thinks that either Bobert or BillD thinks, therefor leaving some uncertainty as to whether either of them actually "is." Had Descartes said "I stink therefore I am" perhaps Chongo would be the only one of us here, since there would at leaste be an element inherent certainty in the premise.

John