Commentary Par XVII 142

The poet surely forgets what he has not said at [Par XVII 92-93].  If ever there existed a 'proof that remains obscure,' that lacuna qualifies.

This canto, with its lavish praise of Cangrande, may be thought of as Dante's farewell to Verona, written between 1317 and 1318 according to Petrocchi (Petr.1988.2), pp. 335, 337.  For the question, still somewhat vexed, of the exact date of Dante's arrival in Ravenna (we assume soon after he left Verona), see Eugenio Chiarini, 'Ravenna' (ED.1973.4), pp. 861-64.