Perhaps you should try some spelling variations:
learning inequality » earnings inequality, measuring inequality, deepening inequality
garding inequality » garding's inequality, earnings inequality, hardy 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 (garding inequality))) OR (learning quality)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(wage OR wave) and ((((learning inequality) or (garding inequality))) or (learning quality))".
• Adding a wildcard symbol may retrieve word variants: (wage OR wave) and ((((learning inequality) or (garding inequality))) or (learning quality))*.