def er_innenfor(tallene):
    innenfor = True
    for tall in tallene:
        if tall<=10 or tall>=20:
            innenfor = False
    return innenfor

assert er_innenfor([19, 11, 16])
assert not er_innenfor([17, 1, 15])
assert not er_innenfor([17, 10, 15])
assert not er_innenfor([17, 20, 15])
assert er_innenfor([15])
assert not er_innenfor([1])
assert er_innenfor([])