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Note that R $^{10 }$and R $^{11 }$are as defined above. 

Examples of the monomer from which recurring units (a2) are derived are given below. 

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Note that R $^{12 }$and R $^{13 }$are as defined above. 

The acid labile groups represented by R $^{11 }$and R $^{13 }$in for- mula (3) may be selected from a variety of such groups. The acid labile groups may be the same or different and preferably include groups of the following formulae (A-1) to (A-3). 

In formula (A-1), RL $^{30 }$is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in which each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group of formula (A-3). Exemplary tertiary alkyl groups are tert-butyl, tert- amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclo› pentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl, l-ethyl-2-cy› clopentenyl, l-ethyl-2-cyclohexenyl, and 2-methyl-2- adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl, triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2-oxooxan- 4-yl, and 5-methyl-2-oxooxolan-5-yl. Letter Al is an integer ofO to 6. 

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(A-1) 

(A-2) 

(A-3) 

