corollary about signs of products of transposition
sign-of-cycle proposition
Added an example on the sign of product of cycles
added order notation
added definition of subgroup
added examples of subgroups
added prop:subgroup-criterion
fixed \MZ in place of \MB{Z}
added example usage of subgroup criterion
added prop:subgroup-ops
added rem:join
added def:generator, shortcut \gen
added /gen shortcut
added prop:generator-is-subgroup