Perhaps you should try some spelling variations:
"generation theorem" » "generation theory", "separation theorem", "preparation theorem"
"operator theory" » "operation theory"
"operators theory" » "operations 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: (((("operator theory") OR ("operators theory"))) OR ("generation theorem")).
• Removing quotes may allow a broader search: (((( operator theory ) or ( operators theory ))) or ( generation theorem )).
• Adding a wildcard symbol may retrieve word variants: (((("operator theory") or ("operators theory"))) or ("generation theorem"))*.