Olivetti portable typewriters Lettera series

Olivetti made a series of portable typewriters with the name "Lettera", and a number.

Usually, the number or word after the word "Letter" didn't make much sense.
Except for Lettera 22, which after the name indicated the twenty-second letter, after the 21 letters of the classical alphabet.
Also "Dora" (a woman's name and the name of the river that passes through Ivrea, the city of Olivetti's headquarters), College (intended for students), and others.

Here there are some documents about these. Mostly in Italian, since it's from Olivetti for Italian market. But I will add others in the following months.

General advirtisement for the Olivetti portable typewriters. Olivetti has always paid great attention to the presentation of its products

Olivetti Class, leaflet (1989)
Olivetti College, leaflet (1975)
Olivetti Lettera 22 (1950)
Olivetti Lettera 27, leaflet (1989)
Olivetti Lettera 31T, leaflet (1989)
Olivetti Lettera 35, leaflet (1972)
Olivetti Lettera 35 another leaflet (1972)
Olivetti Lettera 32, leaflet (1970)
Olivetti Lettera 40/41/42 and Lettera 50/51/52, a general presentation (1980). It used a particular ribbon cartridge.
Olivetti Lettera 62, leaflet (1989)
Olivetti Lettera 92, leaflet (1989)
Olivetti Tropical, a leaflet (1984)
Olivetti Tropical, another leaflet (1984)

Could be that there are other documents in other pages, if there is a page with a specific Olivetti model.