typo in thm:trans-prod
Errata for dfc3248, unmarked
Revert "fixed bracketing" because it breaks the ebook version.

This reverts commit ea6bd86c3ea642485eb208f8c0a4eb5c1e799345.
improved \prd and \sm magic
Merge pull request #489 from TimRichter/typothm264

Typo thm:trans-prod
mark errata for dfc3248
manual reflowing of W_s
Merge pull request #490 from mikeshulman/prdmagic

improved \prd and \sm magic