Perhaps you should try some spelling variations:
approches interdisciplinaires » approaches interdisciplinary, approccio interdisciplinare, approcci interdisciplinari
approach interdisciplinary » approccio interdisciplinare, through interdisciplinary, approach multidisciplinary
lettre » lettres

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• If you are trying to use Boolean operators, they must be ALL CAPS: ((approches interdisciplinaires) OR (approach interdisciplinary)) de la lettre.
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