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Inequalities for Moduli of Continuity in Abstract Banach Spaces
Authors:V V Zhuk  G I Natanson
Abstract:Suppose that X is a Banach space, K denotes the set of real numbers R or the set of nonnegative real numbers R {+}, 
$$A\left( K \right) = \left\{ {T_{{\alpha }} } \right\}{\alpha }{\kern 1pt} \in {\kern 1pt} {K}$$
is a family of linear operators from X into X such that T 0=I is the identity operator in X, 
$$T_{\alpha } T_{\beta }$$
for all 
$${\alpha ,\beta } \in K$$
, and there exists M such that 
$$\left\| {T_{\alpha } \left( x \right)} \right\| \leqslant M\left\| x \right\|$$
for all 
$$\alpha \in {\text{K,}}x \in X$$
. The expression 
$$\eta _r \left( {x,h} \right) = \mathop {\sup }\limits_{T_t \in A\left( K \right),\left| t \right| \leqslant h} \left\| {\left( {T_t - I} \right)^r \left( x \right)} \right\|$$
is called the rth order modulus of continuity of an element x with step h in the space X with respect to the family A(K). The properties of 
$$\eta _r \left( {x,h} \right)$$
are studied. Bibliography: 3 titles.
Keywords:
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