Perhaps you should try some spelling variations:
learning inequality » earnings inequality, garding inequality, measuring inequality
warning inequality » earnings inequality, garding inequality, widening inequality
learning quality » learning ability

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (wage OR wave) AND ((((learning inequality) OR (learning quality))) OR (warning inequality)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(wage or wave) and ((((learning inequality) OR (learning quality))) or (warning inequality))".
• Adding a wildcard symbol may retrieve word variants: (wage or wave) and ((((learning inequality) OR (learning quality))) or (warning inequality))*.