Perhaps you should try some spelling variations:
"mathematics and its applications, soviet theories" » "mathematics and its applications, comet theories", "mathematics and its applications, secret theories"
"mathematics and its applications, set theories" » "mathematics and its applications, set theory"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (((("mathematics and its applications, soviet theories") OR ("mathematics and its applications, set theories"))) OR ("mathematics and its application, soviet theory")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"mathematics and its applications, soviet theories\") OR (\"mathematics and its applications, set theories\"))) or (\"mathematics and its application, soviet theory\"))".
• Removing quotes may allow a broader search: (((( mathematics and its applications, soviet theories ) OR ( mathematics and its applications, set theories ))) or ( mathematics and its application, soviet theory )).
• Adding a wildcard symbol may retrieve word variants: (((("mathematics and its applications, soviet theories") OR ("mathematics and its applications, set theories"))) or ("mathematics and its application, soviet theory"))*.