Akademik

не иначе как
НЕ ИНАЧЕ (КАК)
[restr Particle; these forms only; var. without как is often parenth; var. with как always precedes the word, phrase, or clause to which it refers; fixed WO]
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used to express the speaker's belief that his (or, occas., another's) supposition is correct, even though he does not know it for a fact:
- must [+ infin];
- I am <he is etc> sure (certain);
- without a doubt;
- no doubt;
- (that's) for sure <for certain>;
- (there's) no doubt about it <that>;
- [in limited contexts] I bet.
     ♦ Илья вошёл в избу запыхавшись - не иначе как бежал... (Абрамов 1). Ilya came into the house out of breath-he must have run (1b).
     ♦ [Булычов:] Пропьют государство. [Башкин:] Не иначе (Горький 2). [В.:] ТЪеу'П sell the state for a drink. [B.:] For certain (2b).

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.