Make fields in a layout un-editable when two fields are not identical
Basically I have a database which keeps entries version controlled based upon two fields 'Version' and 'VersionOf' (e.g. Version 4 of 5). I wish to make all previous versions, i.e. any records where Version != VersionOf, un-editable such that users can't go back and change things that they previously entered. They can only edit the latest version, or add a new version.
How would I do this?