Perhaps you should try some spelling variations:
"alternative theory" » "alternative theories", "alternative therapy"
"operations theory" » "operators theory", "observations theory", "operator theory"
"operation theory" » "operator theory", "iteration theory", "generation theory"

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: (((("operation theory") OR ("operations theory"))) OR ("alternative theory")).
• Removing quotes may allow a broader search: (((( operation theory ) or ( operations theory ))) or ( alternative theory )).
• Adding a wildcard symbol may retrieve word variants: (((("operation theory") or ("operations theory"))) or ("alternative theory"))*.