> intsfrom n == n : intsfrom (n + 1)

> notdiv a == { x -> x % a /= 0 }

> filter f [] == []
> filter f (a : b) == a : filter f b <| f a |> filter f b

> era (a : b) = a : era (filter (notdiv a) b)

era (intsfrom 2)
era (2: (intsfrom 3))
2: era (filter (notdiv 2) (intsfrom 3))
2: era (filter (notdiv 2) (3: (intsfrom 4)))
2: era (3: filter (notdiv 2) (intsfrom 4))
2: 3: era (filter (notdiv 3) (filter (notdiv 2) (intsfrom 4)))
2: 3: era (filter (notdiv 3) (filter (notdiv 2) (4: (intsfrom 5))))
2: 3: era (filter (notdiv 3) (filter (notdiv 2) (intsfrom 5)))
2: 3: era (filter (notdiv 3) (filter (notdiv 2) (5: (intsfrom 6))))
2: 3: era (filter (notdiv 3) (5: filter (notdiv 2) (intsfrom 6)))
2: 3: era (5: filter (notdiv 3) (filter (notdiv 2) (intsfrom 6)))
2: 3: 5: era (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 6))))
2: 3: 5: era (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (6: (intsfrom 7)))))
2: 3: 5: era (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 7))))
2: 3: 5: era (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (7: (intsfrom 8)))))
2: 3: 5: era (filter (notdiv 5) (filter (notdiv 3) (7: (filter (notdiv 2) (intsfrom 8)))))
2: 3: 5: era (filter (notdiv 5) (7: (filter (notdiv 3) (filter (notdiv 2) (intsfrom 8)))))
2: 3: 5: era (7: (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 8)))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 8)))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (8: (intsfrom 9))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 9)))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (9: (intsfrom 10))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (9: (filter (notdiv 2) (intsfrom 10))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 10)))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (10: (intsfrom 11))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 11)))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (11: (intsfrom 12))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (11: (filter (notdiv 2) (intsfrom 12))))))
2: 3: 5: 7: era (filter (notdiv 7) (filter (notdiv 5) (11: (filter (notdiv 3) (filter (notdiv 2) (intsfrom 12))))))
2: 3: 5: 7: era (filter (notdiv 7) (11: (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 12))))))
2: 3: 5: 7: era (11: (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 12))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 12))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (12: (intsfrom 13)))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 13)))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (13: (intsfrom 14))))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (13: (filter (notdiv 2) (intsfrom 14))))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (13: (filter (notdiv 3) (filter (notdiv 2) (intsfrom 14))))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (filter (notdiv 7) (13: (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 14))))))))
2: 3: 5: 7: 11: era (filter (notdiv 11) (13: (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 14))))))))
2: 3: 5: 7: 11: era (13: (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 14))))))))
2: 3: 5: 7: 11: 13: era (filter (notdiv 13) (filter (notdiv 11) (filter (notdiv 7) (filter (notdiv 5) (filter (notdiv 3) (filter (notdiv 2) (intsfrom 14))))))))
...etc...