Suppose we know the following theorem
Let , satisfy the Possion equation in . Then and if , we have
- ,
- ,
Use the above theorem and cut-off function
,
when and when
to prove the interior holder estimate of possion equation
Let be a domain in , in . If and , then and for any two concentric balls , we have
WLOG assume , let , is the cut off fuction.
then .
Since has compact support, we have representation
Let
Then from the representation. We will bound them respectively.
For , note that , and theorem 4.5 implies
So satisfies (1)
For , since when , we get that in fact
Since we have when and , this means
So satisfies (1)
For , by the same reason,
Apply the Green identity on the domin
So we can estimate as , which means also satisfies (1).
Gilbarg Trudinger’s book. chapter 4, exercise 4.3.