To clear up these things the best remedy is to discuss amongst yourselves all members regularly all our books in classes, then these doubts will be killed. Without reading books it becomes hackneyed and such obnoxious ideas trouble us: Revision history
Diff selection: Mark the radio buttons of the revisions to compare and hit enter or the button at the bottom.
Legend: (cur) = difference with latest revision, (prev) = difference with preceding revision, m = minor edit.