Minor changes: Add helper theorem in_of_diff, reprove L2S_diff without bad theorem L2S_delete1, using new helper theorem.
Minor changes: Add helper theorem in_of_diff, reprove L2S_diff without bad theorem L2S_delete1, using new helper theorem.

git-svn-id: 9ecf60ce9baff443e30a0472d3fd222fcb8117cf@9522 7b97033b-253e-4a5c-9b07-e25f9089a9fd

KestrelInstitute/Specware,KestrelInstitute/Specware,KestrelInstitute/Specware,KestrelInstitute/Specware,KestrelInstitute/Specware