The professor explained the problem and solution 'thereof'. [=the problem and the solution of the problem]
A will or any part 'thereof' [=any part of a will] may be revoked by a subsequent will.
The problem is money, or (a/the) 'lack thereof'. [=the problem is a lack of money]
(..) Management for the building says this space hasn't been officially rented yet. The county recorder has no listing for a Consumer Recreation Service or any derivation thereof. The divers, they're still looking for the cab. As soon as they find it they'll pull the plates and the VIN. Have you spoken (..)1997 The Game