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7/21/2019 serrin theory
1/2
7/21/2019 serrin theory
2/2
1 0 5 6
MATHEMATICS:
MEYERS
AND
SERRIN P R O C .
N .
A .
S .
T h i s r e s u l t i s a n
i m m e d i a t e
c o n s e q u e n c e
o f t h e
f o l l o w i n g
m o r e
g e n e r a l p r o p o s i t i o n .
L E M M A . I f u
=
u ( x )
h a s
d i s t r i b u t i o n d e r i v a t i v e s u p t o
o r d e r
m i n Q
w h i c h a r e
l o c a l l y i n L P , t h e n f o r
e a c h
E> 0 t h e r e
e x i s t s
a f u n c t i o n v
=
v ( x )
i n
C ( Q ) s u c h
t h a t
u
-
v
i s i n W m ' - ( Q ) a n d
I f U
-
V | |
W m . , 0 )
< E .
P r o o f :
L e t
Q ,
b e
t h e o p e n
s e t d e f i n e d b y
u p
=
x
x E | 2 ,
l
x
< v , d i s t a n c e x , 6 i )
>
1 / v } ,
w h e r e
v
= 1 ,
2
. .
F o r
c o n v e n i e n c e w e a l s o d e f i n e
g o
a n d
i L
t o b e n u l l s e t s .
No w
l e t
E 0 .
1 b e a
p a r t i t i o n o f u n i t y o n
Q s u c h
t h a t
s u p p
,
C
Q u a-
Q
, 1 ,
v
1 ,
2
A l s o ,
l e t
K ,
=
K , ( x )
b e
a
C O
m o l l i f i e r
s a t i s f y i n g t h e t w o c o n d i t i o n s
s u p p
K
C
{ x |
J x j