Perhaps you should try some spelling variations:
"characterization classes" » "characterization case", "characterization closed", "characterizations causes"
"characteristics classes" » "characteristic classes", "characteristics causes", "characteristic class"

Try widening your search to All Fields.

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: (("characterization classes") OR ("characteristics classes")).
• Removing quotes may allow a broader search: (( characterization classes ) or ( characteristics classes )).
• Adding a wildcard symbol may retrieve word variants: (("characterization classes") or ("characteristics classes"))*.