Complex sentence: In 1950, Roger Lyndon proved the existence of equations holding in RRA that did not hold in RA, that is, the variety generated by RRA is a proper subvariety of the variety RA.
Split into simpler sentences: In 1950, Roger Lyndon proved the existence of equations holding in RRA that did not hold in RA. Hence the variety generated by RRA is a proper subvariety of the variety RA.