Perhaps this item is relevant: http://www.google.com/url?sa=t&source=web&cd=10&ved=0CFgQFjAJ&url=http%3A%2F%2Fwww.ams.org%2Fnotices%2F200811%2Ftx081101370p.pdf&rct=j&q=mathematical%20formal%20proof%20code%20errors%20papers%20hales&ei=sa9ZTa3TFcOhtwfRuJ3YDA&usg=AFQjCNFIC-BmFLkyHS-B-EgmcLlVT9eFJw&sig2=lrXeg5yk1_EpV_o6ylC7hQ&cad=rjahttp://www.ams.org/notices/200811/tx081101370p.pdf
And another item: Lamport's "structured proofs": http://research.microsoft.com/en-us/um/people/lamport/pubs/lamport-how-to-write.pdf
