... compact Dinh It 1. 2.3 Toan ta c16ngnh5't I tren kh6ng gian Banach X lil compact va chI X lil huu h~n chi~u 1. 3 rich chap Ki hi~u 11 .11 1' lil ChUaH kh6ng gian L", (l s P s 00) Dinh 1Y 1. 3 .1 Gii sli ... \n/2-Jr(t).exp(itx)dt, Ne'u f E J}(RI1) thl Ne'u f E x E Rn f chlfa ch~c t6n t;:~i, c~(w)hl f E L1(W)nL2(W) va t f(x)= f(x), Vx E W Jlinh If 1. ~J V oi m6i f E I} (R 11 ), ta co th~...