/ðeɚˈʌv/ adv
formal : of the thing that has been mentioned
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]
Useful english dictionary. 2012.