Perhaps you should try some spelling variations:
"principio da verdade material" » "principio da estado material" (Expand Search), "principio de verdade material" (Expand Search), "principios de verdade material" (Expand Search), "principio la verdad material" (Expand Search), "principio de verdad material" (Expand Search), "principio da liberdade material" (Expand Search)
principio y » principio de (Expand Search), principio do (Expand Search), principios de (Expand Search)
"Principio y verdad material" » "Principio la verdad material" (Expand Search), "Principio de verdad material" (Expand Search)

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• Performing a fuzzy search may retrieve terms with similar spellings: (("Principio y verdad material") OR ("principio da verdade material"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"Principio y verdad material\") OR (\"principio da verdade material\"))".
• Removing quotes may allow a broader search: (( Principio y verdad material ) OR ( principio da verdade material )).
• Adding a wildcard symbol may retrieve word variants: (("Principio y verdad material") OR ("principio da verdade material"))*.