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polymerizable unsaturated bond and a fluorosulfonic acid and specifically, a polymer comprising recurring units hav› ing the formula (al) or (a2). It is noted that recurring units having the formula (al) or (a2) are simply referred to as recurring units (al) or (a2), hereinafter. 

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[0041] Herein RA is hydrogen or methyl. X 1 is a single bond or ester group. X 2 is a C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene group or CcC$_{10 }$ arylene group, any meth› ylene moiety in the alkylene group may be substituted by an ether moiety, ester moiety or lactone ring-containing moiety, and at least one hydrogen in the group X $^{2 }$is substituted by iodine. X 3 is a single bond, ether group, ester group or C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene group, any methylene moiety in the alkylene group may be substituted by an ether or ester moiety. Rf$^{1 }$to Rf$^{1 }$are each independently hydrogen, fluorine or trifluoromethyl at least one of Rf 1 to R:t4 is fluorine or trifluoromethyl, and Rf $^{1 }$and Rf may bond together to form a carbonyl group. R 1 to Rs are each independently a C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{12 }$ straight, branched or cyclic alkenyl group, C$_{2}$-C$_{12 }$ straight, branched or cyclic alkynyl group, CcC$_{20 }$ aryl group, C$_{7}$ -C$_{12 }$ aralkyl group, or C$_{7}$ -C$_{12 }$ aryloxyalkyl group, in which at least one hydrogen ( one or more or even all hydrogen atoms) may be substituted by hydroxyl, car› boxyl, halogen, oxo, cyano, amide, nitro, sultone, sulfone or sulfonium salt-containing moiety, and in which any meth› ylene moiety may be substituted by an ether, ester, carbonyl, carbonate or sulfonate moiety. Also, R 1 and R 2 may bond together to form a ring with the sulfur atom to which they are attached. 

[0042] Preferably, the recurring units (al) and (a2) are represented by the formulae (al-1) and (a2-l), respectively. 

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[0043] Herein RA, R 1 to Rs, Rf 1 to Rf\ and X 1 are as defined above. R 6 is a C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkyl group, halogen atom exclusive of iodine, hydroxyl group, C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkoxy group, or C$_{2}$-Cs straight, branched or cyclic alkoxycarbonyl group, m is an integer of 1 to 4, and n is an integer of Oto 3. 

[0044] Examples of the anion moiety in the monomer from which recurring units (al) or (a2) are derived are given below, but not limited thereto. 

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