Perhaps you should try some spelling variations:
"ill-mixed problems" » "ill-wicked problems", "ill-based problems"
"ill-mixed problem" » "ill-based problem"
"ill-posed problems" » "ill-pose problems"

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: (("ill-mixed problem") OR ((("ill-posed problems") OR ("ill-mixed problems")))).
• Removing quotes may allow a broader search: (( ill-mixed problem ) or ((( ill-posed problems ) or ( ill-mixed problems )))).
• Adding a wildcard symbol may retrieve word variants: (("ill-mixed problem") or ((("ill-posed problems") or ("ill-mixed problems"))))*.