The man who reaches R0 does not yet see it.
A virus caused its citizens to abandom the ground a long· time ago. Thin Babels rise today from the earth at a great distance from one another, blurred in the cloucls, supporting the city.
Spiralling· towards the sky, each Babel has a hollow centre, deep as a well; from there, looking down, the citizens contemplate, fascinated, the lost ground and the monuments of a past era.
A formula determines life and rhythms in R0: when its value is minor than one, life flows horizontally between the connected Babels. When it excesses one, each Babel closes in itself like a shell, providing· life and sustainment to its inhabitants.
A description of R0 should include all its past: the city reveals it, contains it, and teils it as lines of a hand.