> Right. Essentially, if the ø (sometimes called ø2) resulting from
> both i- AND u-umlaut of a was pronounced differently than the ø
> resulting from i-umlaut of o, then ON had 10 vowels, not 9 (which
> includes the short, long, and long nasalized vesions) ;)
>
> Konrad

Or maybe 13, if you count the more open or lax pronunciation of the
vowels later spelt <u> and <i> (earlier <o> and <e>) in unstressed
possitions?! But these two only short + or - nasal.

Llama Nom