clean up
remove approach 2 to monoids by generators and relations
clean up
abelian groups by generators and relations
sums of abelian groups ...
sums of abelian groups ready for category-theoretic formulation
sums (coproducts) exist in the category of abelian groups

... over any index type
Change "Coproduct" to "Sum"
clean up and timing

: compiling Categories.v ; >Categories.timing \time -f "%U sec, %M bytes: Categories" coqc   -R . Ktheory -no-native-compiler -indices-matter -time  Categories
2.75 sec, 1471496192 bytes: Categories
./Categories.v:71868-71872: [Qed.] 0.358 secs (0.357u,0.s)
./Categories.v:27450-27454: [Qed.] 0.258 secs (0.256u,0.s)
./Categories.v:79263-79271: [Defined.] 0.17 secs (0.169u,0.s)
./Categories.v:20028-20032: [Qed.] 0.112 secs (0.112u,0.s)
./Categories.v:74123-74268: [exact~~(ap~f~(universalMarkedA...] 0.069 secs (0.069u,0.s)
./Categories.v:71571-71708: [exact~~(Monoid.multproperty~f~...] 0.066 secs (0.065u,0.s)
./Categories.v:71726-71863: [exact~~(Monoid.multproperty~g~...] 0.062 secs (0.062u,0.s)
./Categories.v:27388-27449: [exact_op~(assoc~_~_~_~_~_~(Sum...] 0.053 secs (0.052u,0.001s)
./Categories.v:80120-80128: [Defined.] 0.051 secs (0.051u,0.s)
./Categories.v:16936-16959: [End~StandardCategories.] 0.039 secs (0.035u,0.004s)