Key legal question
Whether the respondents could invoke, by exception, the reduction of a fideicommissary substitution without first challenging the 1983 partition agreement under contract-avoidance rules.
Extracted holding
Yes. The respondents could rely on the exception under Art. 533(3) CC; no prior invalidation of the partition agreement was required.
Extracted reasoning
The reserve is infringed by the fideicommissary substitution itself, not by the partition agreement. A waiver of the reduction exception requires a clear declaration; none was established.