・Corrected a misprint in the fifth paragraph of \S I1 ("may be only be understood" --->
　"may only be understood")

・Corrected a misprint in Remark 1.9.4 ("as in well-known" ---> "as is well-known")

・Corrected a misprint in Remark 1.9.8 ("[arithmetic] fundamental of" --->
　"[arithmetic] fundamental group of")

・Corrected four misspellings ("rectange") of the word "rectangle" in \S 2

・Corrected four instances of a misprint ("to the denote" ---> "to denote") in 
　Definitions 3.1, (iii); 4.1, (iii)

・Corrected two instances of a misprint ("is defined be" ---> "is defined to be") 
　in Definition 5.3, (i), (ii)

・Slightly reworded a phrase in Definition 5.3, (i) ("glue together to form" ---> "together form") 

・Added an explanatory phrase in the discussion following the first display of Definition 5.4, (iii)

・Updated the Acknowledgements

・Corrected a slight error in the second display of Definition 5.1, (ii), and the preceding
　discussion