about LZMA SDK license

Hi, all

7-zip has a sdk: LZMA SDK.
webpage: http://www.7-zip.org/sdk.html

About its license: "LZMA SDK is placed in the public domain."
What's mean?

If we use it in our project. Which restriction?

7-zip license is here:
http://www.7-zip.org/license.txt

Regards.

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Quan Zongliang
quanzongliang@gmail.com
CIT JAPAN: http://www.cit.co.jp
CIT CHINA: http://www.citbj.com.cn