Fix math typo and add link.
Fix math typo and add link.

Fuuzetsu/haddock,Fuuzetsu/haddock,Helkafen/haddock,idontgetoutmuch/haddock,Fuuzetsu/haddock,niteria/haddock,idontgetoutmuch/haddock,haskell/haddock,idontgetoutmuch/haddock,haskell/haddock,haskell/haddock,niteria/haddock,niteria/haddock,Helkafen/haddock,Helkafen/haddock,Fuuzetsu/haddock,haskell/haddock,haskell/haddock