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The lactone structural part may have or may not have a substituent (Rb$_{2}$ ). As preferred substituents (Rb 2 ), an alkyl group having from 1 to 8 carbon atoms, a cycloalkyl group having from 4 to 7 carbon atoms, an alkoxyl group having from 1 to 8 carbon atoms, an alkoxycarbonyl group having from 2 to 8 carbon atoms, a carboxyl group, a halogen atom, a hydroxyl group, a cyano group, and an acid-decomposable group are exemplified, and more preferred substituents are an alkyl group having from 1 to 4 carbon atoms, a cyano group, and an acid-decomposable group. n$_{2 }$ represents an integer of 0 to 4. When n$_{2 }$is 2 or more, each substituent may be the same with or different from every other substituent. A plurality of substituents (Rb$_{2}$ ) may be bonded to each other to form a ring. 

As repeating unit having a lactone structure, a repeating unit represented by the following formula (All) is preferred. 

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In formula (All), Rb$_{0 }$ represents a hydrogen atom, a halo› gen atom, or an alkyl group having from 1 to 4 carbon atoms. As the examples of preferred substituents that the alkyl group represented by Rb$_{0 }$may have, a hydroxy 1 group and a halogen atom are exemplified. As the halogen atom represented by Rb 0, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are exemplified. Rb$_{0 }$ preferably represents a hydrogen atom, a methyl group, a hydroxymethyl group, or a trifluoromethyl group, and especially preferably a hydrogen atom or a methyl group. 

Ab represents a single bond, an alkylene group, a divalent linking group having a monocyclic or polycyclic alicyclic hydrocarbon structure, an ether bond, an ester bond, a carbo› nyl group, or a divalent group of combining these groups, and preferably a single bond or a linking group represented by -Ab$_{1}$ -C0$_{2}$ -. 

Ab $_{1 }$represents a straight chain or branched alkylene group, or a monocyclic or polycyclic cycloalkylene group, and pref› erably a methylene group, an ethylene group, a cyclohexylene group, an adamantylene group, or a norbomylene group. 

V represents a group having a lactone structure. Specifi› cally, V represents a group having a structure represented by any of formulae (LCl-1) to (LCl-17). 

Of the repeating units represented by formula (All), as repeating units having an especially preferred lactone group when Ab represents a single bond, the following repeating units are exemplified. In the specific examples, Rx represents H, CH$_{3}$ , CH$_{2}$0H, or CFy 

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