Right, so, in Rune's roof scene Arvo is thinking about non-linearity in a whimsical way that isn't supposed to make much sense, I think - he's just experiencing a case of deja-vu, feeling the same way he did long time ago, that sense of inspired hope for the future and closeness to someone he mutually appreciates, as if the life looped back on itself and the same moment happened twice.
And... I don't quite remember what Mikko said about non-linearity. Could you remind me when he said it so I can double-check?