Perhaps you should try some spelling variations:
deberes fiduciario » deveres fiduciarios (Expand Search), deber fiduciario (Expand Search), derechos fiduciarios (Expand Search)
"Deberes fiduciario en administrador" » "Deberes fiduciario el administrador" (Expand Search), "Deberes fiduciario un administrador" (Expand Search), "Deberes fiduciario ente administrador" (Expand Search), "Deberes fiducia en administrador" (Expand Search)
"Deberes fiduciarios del administrador" » "Deberes fiduciarios de administrador" (Expand Search), "Deberes fiduciario de administrador" (Expand Search), "Deberes fiduciarios a administrador" (Expand Search)

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• Performing a fuzzy search may retrieve terms with similar spellings: (("Deberes fiduciarios del administrador") OR ("Deberes fiduciario en administrador"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"Deberes fiduciarios del administrador\") OR (\"Deberes fiduciario en administrador\"))".
• Removing quotes may allow a broader search: (( Deberes fiduciarios del administrador ) OR ( Deberes fiduciario en administrador )).
• Adding a wildcard symbol may retrieve word variants: (("Deberes fiduciarios del administrador") OR ("Deberes fiduciario en administrador"))*.