, .
x x 0.
. (1) - [a;b] -, (1) - [a;b], S(x) [a;b].
-: - . [a;b]. - , (a;b). -, S(x)= , . < (2), [a;b]. -, (1) - [a;b], . n [a;b] < (3), = . , n= (3) : < (4). , x= < (5). - (x) -. - [a;b] < (6). . - S(x)-S()=(S(x)- (x))+( (x)- ())+( ()-S()). , . (4)-(6) - : < , [a;b], . - (2). - S(x) [a;b].