Perhaps you should try some spelling variations:
utilisateurs informatique » ordinateur informatique
mathematical development » statistical development, theoretical developments, mathematical treatment
theoretical development » theoretical developments, cortical development, political development
basic iron » basic ion, basic iban

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((mathematical development) OR (theoretical development)) basic iron utilisateurs informatique~".
• Adding a wildcard symbol may retrieve word variants: ((mathematical development) OR (theoretical development)) basic iron utilisateurs informatique*.