What is the difference between "As is mentioned" and "As mentioned"?
For example,
1. As is mentioned in Section I, Chiba is a prefecture of Japan.
2. As mentioned in Section I, Chiba is a prefecture of Japan.

What is the difference between the above sentences 1 and 2?

Question

What is the difference between "As is mentioned" and "As mentioned"?
For example, 
1. As is mentioned in Section I, Chiba is a prefecture of Japan.
2. As mentioned in Section I, Chiba is a prefecture of Japan.

What is the difference between the above sentences 1 and 2?

Answer

There's no difference. You can say it either way.

Answer

Thank you for your comment. I'm glad to hear that (^^)/

Answer

The fist to be how it were mentioned until now and the second to be how neither it were mentioned in a past but not now, this second could to be used if you will say something that  show up contrast to the initial idea, exemple:

"As mentioned in Section I, Chiba is a prefecture of Japan, but...(show up other idea)"

Would be more convenient if you've used "on" instead "of", because it could seggest that Chiba would be prefecture of all Japan. ^^

Good lucky with English. Im fan of your country culture.