Perhaps you should try some spelling variations:
"differential equation" » "differential equations"
"difference equationss" » "difference equation", "differences equations", "differenced equations", "differential equationss"
"difference equations" » "differential equations"

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: (("differential equation") OR ((((("difference equationss") OR ("difference equations"))) OR ((("difference equationss") OR ("difference equations")))))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"differential equation\") or (((((\"difference equationss\") OR (\"difference equations\"))) or (((\"difference equationss\") OR (\"difference equations\"))))))".
• Removing quotes may allow a broader search: (( differential equation ) or ((((( difference equationss ) OR ( difference equations ))) or ((( difference equationss ) OR ( difference equations )))))).
• Adding a wildcard symbol may retrieve word variants: (("differential equation") or ((((("difference equationss") OR ("difference equations"))) or ((("difference equationss") OR ("difference equations"))))))*.