On diffeological principal bundles of non-formal pseudo-differential operators over formal ones.

We describe the structure of diffeological bundle of non formal classical pseudo-differential operators over formal ones, and its structure group. For this, we give results on diffeological principal bundles with (a priori) no local trivialization including an Ambrose-Singer theorem, use the smoothing connections alrealy exhibited by the author in previous works, and finish with open questions. [ABSTRACT FROM AUTHOR]