・Modified \S 1.7 and added the references [Bell], [Dawson] to the Bibliography
・Deleted the hyphen following "non" for "nonzero", "noncommutative", and "nonconstant"
・Slightly modified the explanations at the beginning of \S 2.7, (ii), and the beginning
and middle of \S 2.7, (iv)
・Modified and extended the discussion of \S 2.8
・Modified and extended the discussion at the final portions of \S 3.3, (ii), (vii)
・Corrected a misprint ("scheme-theory" ---> "scheme theory") in \S 4.1, (i)
・Added item "(v)" to \S 4.1