**Thm:** Suppose , then there exists a constant such that

for all , where . For functions in , we have

**Thm:** Suppose is bounded domain in , and . Assume and , there exists one version , for , such that

**Remark:** This is critical number. For , we can choose . Consider the function on the unit ball . Then

if and only if , which is .

However consider the which is

So .

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