(A-v) A polymer comprising recurring units represented by the following general formula (2a???): wherein R4 is hydrogen or methyl, R5 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, R6 is an acid labile group, R6a is hydrogen or an acid labile group, R6a being at least partially an acid labile group, x is 0 or a positive integer, y is a positive integer, satisfying x+y???5, t