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张恭庆泛函分析题—数 计 院—张 秀 洲
课后习题解答与辅导
张 秀 洲
二 0 0 九 年 三 月 一 十 日
1.1.5
1.1.6
1.1.7
1.2.2
1.2.3
1.2.4
1.3.3
1.3.4
1.3.5
1.3.7
1.3.8
1.3.9
1.4.1
1.4.5-6
1.4.9
1.4.11
1.4.12
1.4.13
1.4.14
1.4.15
1.4.17
1.5.1证明:(1) (Þ) 若xÎint(E),存在d > 0,使得Bd (x) Í E.
注意到x + x/n ® x ( n ® ¥ ),故存在N Î N+,使得x + x/N Î Bd (x) Í E.
即x/( N/( 1 + N ) ) ÎE.因此P(x) £ N/( 1 + N ) < 1.
(Ü) 若P(x) < 1.则存在a > 1,使得y = a xÎE.因qÎint(E),故存在d > 0,使得Bd (q) Í E.令h = d (a - 1)/a,"zÎBh (x),令w = (a z - y )/(a - 1),
则|| w || = || (a z - y )/(a - 1) || = || a z - y ||/(a - 1)
= || a z - a x ||/(a - 1) = a || z - x ||/(a - 1) < ah/(a - 1) = d.
故wÎBd (q) Í E.故z = ((a - 1)w + y )/a Î E,因此,Bh (x) Í E.所以xÎint(E).
(2) 因int(E) = E,故有cl(int(E)) Í cl(E).下面证明相反的包含关系.
若xÎcl(E),则"e > 0,存在yÎE,使得|| x - y || < e/2.
因ny/(n + 1) ® y ( n ® ¥ ).故存在N Î N+,使得|| Ny/(N + 1) - y || < e/2.
令z = Ny/(N + 1),则zÎE,且P(z) £ N/(N + 1) < 1,
由(1)知z Îint(E).而|| z - x || £ || z - y || + || y - x || < e/2 + e/2 = e.
故xÎcl(int(E)),因此cl(E) Í cl(int(E))所以cl(int(E)) = cl(E).
1.5.3证明:因为C是紧集,所以C是闭集.
因为C是紧集,故C的任意子集都列紧.
而T(C) Í C,故T(C)列紧.
于是,由Schauder不动点定理,T在C上有一个不动点.
[Schauder定理:B*空间中闭凸集C上使T(C)列紧的连续自映射T必有不动点]
1.5.4
1.5.5证明:设C = {x = (x1, x2, ..., xn)ÎRn | å 1 £ i £ n xi = 1,xi ³ 0 ( i = 1, 2, ..., n) }.
则C是有界闭集,且是凸集,因此C是紧凸集.
因为"xÎC,xi 不全为0,而aij > 0,故Ax的各分量也非负但不全为零.
"xÎC,设f (x) = (Ax)/( å 1 £ i £ n (Ax)i ),则f (x)ÎC.
容易验证f : C ® C还是连续的.
由Brouwer不动点定理,存在f的不动点x0ÎC.
即f (x0) = x0,也就是(Ax0)/( å 1 £ i £ n (Ax0)i ) = x0.
令l = å 1 £ i £ n (Ax0)i,则有Ax0 = l x0.
1.5.6证明:设B = { uÎC[0, 1] | ò[0, 1] u(x) dx = 1,u(x) ³ 0 },
则B是C[0, 1]中闭凸集.
设max (x, y)Î[0, 1]´[0, 1] K(x, y) = M,min (x, y)Î[0, 1]´[0, 1] K(x, y) = m,
ò[0, 1] (ò[0, 1] K(x, y) dy) dx = N,max xÎ[0, 1] | ò[0, 1] K(x, y) dy |= P.
令(S u)(x) = (ò[0, 1] K(x, y) u(y) dy)/(ò[0, 1] (ò[0, 1] K(x, y) u(y) dy) dx )
则ò[0, 1] (S u)(x) dx = 1,u(x) ³ 0;
即S uÎB.因此S是从B到B内的映射.
"u, vÎB,
|| ò[0, 1] K(x, y) u(y) dy - ò[0, 1] K(x, y) v(y) dy ||
= || ò[0, 1] K(x, y) (u(y) - v(y)) dy ||
= max xÎ[0, 1] | ò[0, 1] K(x, y) (u(y) - v(y)) dy |
£ M · || u - v ||;
因此映射u # ò[0, 1] K(x, y) u(y) dy在B上连续.
类似地,映射u # ò[0, 1] (ò[0, 1] K(x, y) u(y) dy) dx也在B上连续.
所以,S在B上连续.
下面证明S(B)列紧.
首先,证明S(B)是一致有界集."uÎB,
|| S u || = || (ò[0, 1] K(x, y) u(y) dy )/(ò[0, 1] (ò[0, 1] K(x, y) u(y) dy) dx )||
= max xÎ[0, 1] | ò[0, 1] K(x, y) u(y) dy |/(ò[0, 1] (ò[0, 1] K(x, y) u(y) dy) dx )
£ (M ·ò[0, 1] u(y) dy |/(m ò[0, 1] (ò[0, 1] u(y) dy) dx ) = M/m,
故S(B)是一致有界集.
其次,证明S(B)等度连续."uÎB,"t1, t2Î[0, 1],
| (S u)(t1) - (S u)(t2) |
= | ò[0, 1] K(t1, y) u(y) dy - ò[0, 1] K(t2, y) u(y) dy |/(ò[0, 1] (ò[0, 1] K(x, y) u(y) dy) dx )
£ ò[0, 1] | K(t1, y) - K(t2, y) | u(y) dy /(mò[0, 1] (ò[0, 1] u(y) dy) dx )
£ (1/m) · max yÎ[0, 1] | K(t1, y) - K(t2, y) |
由K(x, y)在[0, 1]´[0, 1]上的一致连续性,
"e > 0,存在d > 0,使得"(x1, y1), (x2, y2)Î[0, 1],只要|| (x1, y1) - (x2, y2) || < d,
就有| K(x1, y1) - K(x2, y2) | < m e.
故只要| t1 - t2 | < d 时,yÎ[0, 1],都有| K(t1, y) - K(t2, y) | < m e.
此时,| (S u)(t1) - (S u)(t2) | £ (1/m) · max yÎ[0, 1] | K(t1, y) - K(t2, y) |
£ (1/m) · m e = e.
故S(B)是等度连续的.
所以,S(B)是列紧集.
根据Schauder不动点定理,S在C上有不动点u0.
令l = (ò[0, 1] (ò[0, 1] K(x, y) u0(y) dy) dx.
则(S u0)(x) = (ò[0, 1] K(x, y) u0(y) dy)/l = (T u0)(x)/l.
因此(T u0)(x)/l = u0(x),T u0 = l u0.
显然上述的l和u0满足题目的要求.
1.6.1 (极化恒等式)证明:"x, yÎX,q(x + y) - q(x - y) = a(x + y, x + y) - a(x - y, x - y)
= (a(x, x) + a(x, y) + a(y, x) + a(y, y)) - (a(x, x) - a(x, y) - a(y, x) + a(y, y))
= 2 (a(x, y) + a(y, x)),
将i y代替上式中的y,有
q(x + i y) - q(x - i y) = 2 (a(x, i y) + a(i y, x))= 2 (-i a(x, y) + i a( y, x)),
将上式两边乘以i,得到i q(x + i y) - i q(x - i y) = 2 ( a(x, y) - a( y, x)),
将它与第一式相加即可得到极化恒等式.
1.6.2证明:若C[a, b]中范数|| · ||是可由某内积( · , · )诱导出的,
则范数|| · ||应满足平行四边形等式.
而事实上,C[a, b]中范数|| · ||是不满足平行四边形等式的,
因此,不能引进内积( · , · )使其适合上述关系.
范数|| · ||是不满足平行四边形等式的具体例子如下:
设f(x) = (x – a)/(b – a),g(x) = (b – x)/(b – a),则|| f || = || g || = || f + g || = || f – g || = 1,
显然不满足平行四边形等式.
1.6.3证明:"xÎL2[0, T],若|| x || = 1,由Cauchy-Schwarz不等式,有
| ò[0, T] e - ( T - t ) x(t ) dt |2 £ (ò[0, T] (e - ( T - t ))2 dt ) (ò[0, T] ( x(t ))2 dt )
= ò[0, T] (e - ( T - t ))2 dt = e - 2T ò[0, T] e 2t dt = (1- e - 2T )/2.
因此,该函数的函数值不超过M = ((1- e - 2T )/2)1/2.
前面的不等号成为等号的充要条件是存在lÎR,使得x(t ) = l e - ( T - t ).
再注意|| x || = 1,就有ò[0, T] (l e - ( T - t ))2 dt = 1.解出l = ±((1- e - 2T )/2) - 1/2.
故当单位球面上的点x(t ) = ±((1- e - 2T )/2) - 1/2 · e - ( T - t )时,
该函数达到其在单位球面上的最大值((1- e - 2T )/2)1/2.
1.6.4证明:若xÎN ^,则"yÎN,(x, y) = 0.而M Í N,故"yÎM,也有(x, y) = 0.
因此xÎM ^.所以,N ^ Í M ^.
1.6.5
1.6.6解:设偶函数集为E,奇函数集为O.
显然,每个奇函数都与正交E.故奇函数集O Í E ^.
"fÎE ^,注意到f总可分解为f = g + h,其中g是奇函数,h是偶函数.
因此有0 = ( f, h) = ( g + h, h) = ( g, h) + ( h, h) = ( h, h).
故h几乎处处为0.即f = g是奇函数.所以有 E ^ Í O.
这样就证明了偶函数集E的正交补E ^是奇函数集O.
1.6.7
证明:首先直接验证,"cÎR,S = {e 2p i n x | nÎZ }是L2[c, c + 1]中的一个正交集.
再将其标准化,得到一个规范正交集S1 = {jn(x) = dn e 2p i n x | nÎZ }.
其中的dn = || e 2p i n x || (nÎZ),并且只与n有关,与c的选择无关.
(1) 当b – a =1时,根据实分析结论有S ^ = {q}.
当b – a <1时,若uÎL2[a, b],且uÎS ^,
我们将u延拓成[a, a + 1]上的函数v,使得v(x) = 0 ("xÎ(b, a + 1]).
则vÎL2[a, a + 1].
同时把S = {e 2p i n x | nÎZ }也看成L2[a, a + 1]上的函数集.
那么,在L2[a, a + 1]中,有vÎS ^.
根据前面的结论,v = q.
因此,在L2[a, b]中就有u = q.
故也有S ^ = {q};
(2) 分成两个区间[a, b – 1)和[b – 1, b]来看.
在[a, b – 1)上取定非零函数u(x) = 1 ( "xÎ[a, b – 1) ).
记pn = ò[a, b – 1) u(x)jn(x) dx.
我们再把u看成是[b – 2, b – 1]上的函数(u在[b – 2, a)上去值为0).
那么pn就是u在L2[b – 2, b – 1]上关于正交集S1 = {jn(x) | nÎZ }的Fourier系数.
由Bessel不等式,ånÎZ | pn |2 < +¥.
再用Riesz-Fischer定理,在L2[b – 1, b]中,ånÎZ pn jn收敛.
并且,若令v = - ånÎZ pn jn,则(v, jn)= - pn (" nÎZ).
设f : [a, b] ® C为:f(x) = u(x) (当xÎ[a, b – 1)),f(x) = v(x) (当xÎ[b – 1, b]).
则f ÎL2[a, b],f ¹ q,
但( f, jn) = ò[a, b – 1) f(x)jn(x) dx + ò[b – 1, b] f(x)jn(x) dx
= ò[a, b – 1) u(x)jn(x) dx + ò[b – 1, b] v(x)jn(x) dx
= pn - pn = 0,
因此,f ÎS1^ = S ^,故S ^ ¹ {q}.
1.6.8证明:( zn/(2p)1/2, zn/(2p)1/2 ) = (1/i)ò| z | = 1 ( zn/(2p)1/2 · (z*)n/(2p)1/2 )/z dz
= (1/(2pi))ò| z | = 1 zn· (z*)n/z dz = (1/(2pi))ò| z | = 1 1/z dz = 1.
若n > m,则n - m - 1 ³ 0,从zn - m - 1而解析.
( zn/(2p)1/2, zm/(2p)1/2 ) = (1/i)ò| z | = 1 ( zn/(2p)1/2 · (z*)m/(2p)1/2 )/z dz
= (1/(2pi))ò| z | = 1 zn· (z*)m/z dz = (1/(2pi))ò| z | = 1 zn - m - 1 dz = 0.
因此,{ zn/(2p)1/2 }n ³ 0是正交规范集.
1.6.9
1.6.10证明:容易验证{en}Ç{ fn}是正交规范集,下面只证明{en}Ç{ fn}是X的基.
"xÎX,由正交分解定理,存在x关于X0的正交分解
x = y + z,其中yÎ X0,zÎ X0^.
因{en}, { fn}分别是X0和X0^的正交规范基,
故y = å nÎN ( y, en ) en,z = å nÎN ( z, fn ) fn.
因zÎ X0^,故(x, en) = ( y + z, en) = ( y, en) + ( z, en) = ( y, en).
因yÎ X0,故(x, fn) = ( y + z, fn) = ( y, fn) + ( z, fn) = ( z, fn).
故x = y + z = å nÎN ( y, en ) en + å nÎN ( z, fn ) fn
= å nÎN ( x, en ) en + å nÎN ( x, fn ) fn.因此{en}Ç{ fn}是X的正交规范基.
1.6.11证明:首先,令j k (z) = (( k +1 )/p)1/2 z k ( k ³ 0 ),
则{ j k }k ³ 0是H 2(D)中的正交规范基.
那么,"u(z)ÎH 2(D),设u(z) = å k ³ 0 a k z k,则"kÎN,有
(u, j k) = òD u(z) · j k(z)* dxdy
= òD (å j ³ 0 a j z j) · j k(z)* dxdy
= å j ³ 0 a j (p/( j +1 ))1/2òD (( j +1 )/p)1/2 z j · j k(z)* dxdy
= å j ³ 0 a j (p/( j +1 ))1/2òD j j(z) · j k(z)* dxdy
= å j ³ 0 a j (p/( j +1 ))1/2 (j j, j k)
= a k (p/( k +1 ))1/2.
即u(z)的关于正交规范基{ j k }k ³ 0的Fourier系数为a k (p/( k +1 ))1/2 ( k ³ 0 ).
(1) 如果u(z)的Taylor展开式是u(z) = å k ³ 0 b k z k,
则u(z)的Fourier系数为b k (p/( k +1 ))1/2 ( k ³ 0 ).
由Bessel不等式,å k ³ 0| b k (p/( k +1 ))1/2 |2 £ || u || < +¥,
于是有 å k ³ 0| b k |2/( k +1 ) < +¥.
(2) 设u(z), v(z)ÎH 2(D),并且u(z) = å k ³ 0 a k z k,v(z) = å k ³ 0 b k z k.
则u(z) = å k ³ 0 a k (p/( k +1 ))1/2j k (z),v(z) = å j ³ 0 b j (p/( j +1 ))1/2j j (z),
(u, v) = ( å k ³ 0 a k (p/( k +1 ))1/2j k (z), å j ³ 0 b j (p/( j +1 ))1/2j j (z) )
= å k ³ 0å j ³ 0 (a k (p/( k +1 ))1/2j k (z), b j (p/( j +1 ))1/2j j (z))
= å k ³ 0å j ³ 0 (a k (p/( k +1 ))1/2 · b j*(p/( j +1 ))1/2) (j k (z), j j (z))
= å k ³ 0 (a k (p/( k +1 ))1/2 · b k* (p/( k +1 ))1/2) = p å k ³ 0 (a k · b k* )/( k +1 ).
(3) 设u(z)ÎH 2(D),且u(z) = å k ³ 0 a k z k.
因1/(1 - z) = å k ³ 0 z k,1/(1 - z)2 = å k ³ 0 (k +1) z k,其中| z | < 1.
故当| z | < 1时,有1/(1 - | z | )2 = å k ³ 0 (k +1) | z | k.
根据(2),|| u(z) ||2 = p å k ³ 0 (a k · a k* )/( k +1 ) = p å k ³ 0 | a k |2/( k +1 ).
|| u ||2/(1 - | z |)2 = (p å k ³ 0 | a k |2/( k +1 )) · ( å k ³ 0 (k +1) | z | k )
³ (p å k ³ 0 | a k |2/( k +1 ) | z | k) · ( å k ³ 0 (k +1) | z | k )
³ p ( å k ³ 0 ( | a k |/( k +1 )1/2 | z | k/2) · ((k +1)1/2 | z | k/2 ))2 (Cauchy-Schwarz不等式)
= p ( å k ³ 0 | a k | · | z | k )2³ p | å k ³ 0 a k z k |2 = p | u(z) |2 ,故| u(z) | £ || u ||/(p1/2 ( 1 - | z | )).
(4) 先介绍复分析中的Weierstrass定理:若{ fn }是区域U Í C上的解析函数列,且{ fn }在U上内闭一致收敛到 f,则f在U上解析.(见龚升《简明复分析》)
回到本题.设{ un }是H 2(D)中的基本列.
则"zÎD,由(3)知{ un(z) }是C中的基本列,因此是收敛列.设un(z) ® u(z).
对C中任意闭集F Í D,存在0 < r < 1使得F Í B(0, r) Í D.
"e > 0,存在NÎN+,使得"m, n > N,都有|| un - um || < e p1/2 ( 1 - r ).
再由(3),"zÎF,
| un(z) - um(z) | £ || un - um ||/(p1/2 ( 1 - | z | )) £ || un - um ||/(p1/2 ( 1 - r )) < e.
令m ® ¥,则| un(z) - u(z) | £ e.这说明{ un }在D上内闭一致收敛到 u.
由前面所说的Weierstrass定理,u在D上解析.
把{ un }看成是L2(D)中的基本列,
因L2(D),故{ un }是L2(D)中的收敛列.设{ un }在L2(D)中的收敛于v.
则v必然与u几乎处处相等.即{ un }在L2(D)中的收敛于u.
因此{ un }在H2(D)中也是收敛的,且收敛于u.所以,H2(D)完备.
1.6.12证明:由Cauchy-Schwarz不等式以及Bessel不等式,"x, yÎX,有
| å n ³ 1 (x, en) · (y, en)* |2 £ (å n ³ 1 | (x, en) |· | (y, en)* | )2
= (å n ³ 1 | (x, en) |· | (y, en) | )2 £ (å n ³ 1 | (x, en) |2) · (å n ³ 1 | (y, en)|2)£ || x ||2 · || y ||2.
因此,| å n ³ 1 (x, en) · (y, en)* | £ || x || · || y ||.
1.6.13证明:(1) 因范数是连续函数,故C = { x Î X | || x - x0 || £ r }是闭集.
"x, y ÎC,因|| x - x0 || £ r,|| x - x0 || £ r },故"lÎ[0, 1],
|| (l x + (1- l) y ) - x0 || = || l ( x - x0 ) + (1- l) (y - x0) ||
£ || l ( x - x0 ) + (1- l) (y - x0) || £ l || x - x0 || + (1- l) || y - x0 || £ l r + (1- l) r = r.
所以,C是X中的闭凸集.
(2) 当x Î C时,y = x.显然y是x在C中的最佳逼近元.
当x Î C时,y = x0 + r (x - x0)/|| x - x0 ||.
"zÎC,|| x - y || = || ( x - x0 - r (x - x0)/|| x - x0 ||) ||
= || (1 - r/|| x - x0 ||) (x - x0) || = || x - x0 || - r.£ || x - x0 || - || z - x0 || £ || x - z ||.
因此,y是x在C中的最佳逼近元.
1.6.14解:即是求e t 在span{1, t, t 2}中的最佳逼近元 (按L2[0, 1]范数).
将{1, t, t 2}正交化为{1, t - 1/2, (t - 1/2)2 - 1/12 } (按L2[0, 1]内积)
再标准化为{j0(t), j1(t), j2(t)},则所求的a k= (e t, j k(t)) = ò[0, 1] e tj k(t) dt,k = 0, 1, 2.
1.6.15证明:设g(x) = (x - a) (x - b)2,则g(a) = g (b) = 0,g’(a) = (b - a)2,g’(b) = 0.
由Cauchy- Schwarz不等式,我们有
(ò[a, b] | f’’(x) |2 dx) · (ò[a, b] | g’’(x) |2 dx) ³ (ò[a, b] f’’(x) ·g’’(x) dx )2.因g’’(x) = 3x - (a + 2b),
故ò[a, b] | g’’(x) |2 dx = ò[a, b] (3x - (a + 2b))2 dx = (b - a)3;
又ò[a, b] f’’(x) ·g’’(x) dx = ò[a, b] (3x - (a + 2b)) · f’’(x) dx = ò[a, b] (3x - (a + 2b))d f’(x)
= (3x - (a + 2b)) · f’(x)| [a, b] - 3ò[a, b] f’(x) dx = 2(b - a);
故(b - a)3 ·ò[a, b] | f’’(x) |2 dx ³ (2(b - a))2 = 4(b - a)2.
所以ò[a, b] | f’’(x)|2 dx ³ 4/(b - a).
1.6.16 (变分不等式)证明:设f (x) = a(x, x) - Re(u0, x).
则f (x) = a(x, x) - Re(u0, x) ³ d || x ||2 - | (u0, x) |
³ d || x ||2 - || u0 || · || x || ³ - || u0 ||2/(4d ) > -¥.
即f在X上有下界,因而f在C有下确界m = inf xÎC f (x).
注意到a(x, y)实际上是X上的一个内积,
记它所诱导的范数为|| x ||a = a(x, x)1/2,则|| · ||a与|| · ||是等价范数.
因此f (x) = a(x, x) - Re(u0, x) = || x ||a2 - Re(u0, x).
设C中的点列{ xn }是一个极小化序列,满足m £ f (xn ) < m + 1/n ( "nÎN+ ).
则由平行四边形等式,
|| xn - xm ||a2 = 2(|| xn ||a2 + || xm ||a2 ) - 4|| (xn + xm)/2 ||a2
= 2( f (xn) + Re(u0, xn) + f (xm) + Re(u0, xm) ) - 4( f ((xn + xm)/2) + Re(u0, (xn + xm)/2))
= 2( f (xn) + f (xm)) - 4 f ((xn + xm)/2) + 2 Re( (u0, xn) + (u0, xm) - (u0, xn + xm) )
= 2( f (xn) + f (xm)) - 4 f ((xn + xm)/2)
£ 2( m + 1/n + m + 1/m ) - 4 m
= 2(1/n + 1/m) ® 0 ( m, n ® ¥ ).
因此|| xn - xm ||2 £ (1/d) || xn - xm ||a2 ® 0 ( m, n ® ¥ ).
即{ xn }为X中的基本列.
由于X完备,故{ xn }收敛.设xn® x0 ( n ® ¥ ).
则|| xn - x0 ||a2 £ M || xn - x0 ||2 ® 0 ( m, n ® ¥ ).
而由内积a( · , · ),( · , · )的连续性,有
a( xn , xn ) ® a( x0 , x0 ),且(u0, xn) ® (u0, x0),( n ® ¥ ).
因此f (xn) = a(xn, xn) - Re(u0, xn) ® a(x0, x0) - Re(u0, x0) = f (x0),( n ® ¥ ).
由极限的唯一性,f (x0) = m = inf xÎC f (x).
至此,我们证明了f 在C上有最小值.下面说明最小值点是唯一的.
若x0, y0都是最小值点,则交错的点列{ x0, y0, x0, y0, x0, ... }是极小化序列.
根据前面的证明,这个极小化序列必须是基本列,
因此,必然有x0 = y0.所以最小值点是唯一的.
最后我们要证明最小点x0ÎC满足给出的不等式.
"xÎC,"tÎ[0, 1],有x0 + t ( x - x0)ÎC,因此有f (x0 + t ( x - x0)) ³ f (x0).
即|| x0 + t ( x - x0) ||a2 - Re(u0, x0 + t ( x - x0)) ³ || x0 ||a2 - Re(u0, x0).
展开并整理得到t Re ( 2a(x0, x - x0) - (u0, x - x0) ) ³ - t2 || x - x0 ||a2.
故当"tÎ(0, 1],有Re ( 2a(x0, x - x0) - (u0, x - x0) ) ³ - t || x - x0 ||a2.
令t ® 0就得到 Re ( 2a(x0, x - x0) - (u0, x - x0) ) ³ 0.
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
2.1.8
2.1.9
2.2.2
2.2.5
2.3.1
2.3.3-2
2.3.4
2.3.5
2.3.7
2.3.8
2.3.9
2.3.11
2.3.12
2.3.13
2.3.14
2.4.4
2.4.5
2.4.6
2.4.7
2.4.8
2.4.9
2.4.10
2.4.11
2.4.12
2.4.13
2.4.14
2.5.4
2.5.5
2.5.7
2.5.8
2.5.10
2.5.12
2.5.18
2.5.20
2.5.22
2.6.1
2.6.2
2.6.3
2.6.4
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