・Slightly modified the text in Fig I.1

・Slightly modified the first ("which" ---> ", which") and second sentences of \S 1

・Slightly modified the first sentence of the second paragraph of \S 1 ("l a prime" ---> "l an {\it odd} prime",
　"discussion preceding [EtTh], Definition 1.7" ---> "discussion at the beginning of [EtTh], \S 2")

・Slightly modified the discussion of "$\Pi_\mu$" in Definition 1.1, (i)

・In Remark 1.1.1, (i), (iv), modified the discussion of the quotient "$\ddot Q$" (which was replaced by the
　quotient "\Pi^{ell}_Y")

・In Remark 1.1.1, (ii), (iii), adjusted the position of the superscripts "$\Th$" and "ell"

・Deleted an unnecessary "$\otimes Z/NZ$" in the notation for the exterior cyclotome in the statement of
　Proposition 1.3, (i)

・Added supplementary references to [AbsTopIII] in the statement of Proposition 1.3, (ii)

・Slightly modified the second reference to [EtTh] in Proposition 1.4

・In Remark 1.4.1, (ii), slightly modified the first sentence, the second display, and the explanations 
　immediately following the second and fourth displays

・Corrected a misprint in Remark 1.6.1 ("[AbsTopI], \S 3" ---> "[AbsTopI], \S 4")

・In the explanation immediately following the final display of Example 1.7, (i), corrected misprints in the 
　subscripts of "$\Phi$" and "calligraphic R" (an unnecessary "i", 3 instances)

・Rewrote the final portion of Example 1.7, (ii), and added references to this rewritten portion of Example 1.7, (ii),
　at the beginning of Example 1.8 and in the final display of Example 1.9, (ii)

・Slightly modified the second sentence of Remark 1.7.1

・Slightly modified the first sentence of Example 1.8, (iv)

・Corrected a misprint in Example 1.8, (v) ("topological groups actions" ---> "topological group actions")

・Corrected a misprint in the first sentence of Example 1.8, (viii) ("(v)" ---> "(iii)")

・Corrected a misprint in the final portion of Example 1.8, (ix)

・Corrected a misprint (a missing comma) in the fourth sentence of Example 1.9, (iv)

・In Remark 1.9.1, corrected misprints (a missing parenthesis in the display; an unnecessary comma in the third 
　sentence following this display) and slightly modified the wording of the two sentences that begin "Put another
　way,"

・Added a supplementary explanatory sentence at the end of Remark 2.1.1, (ii)