因明入正理論疏 1.147

1.147

述曰：此別指法。如立其無常宗，所作性為因。若有處所是常法聚，見非是所作，如虛空等，說名異品。此中既說宗之異品，唯應說云謂若是常，如虛空等。復云見非所作者，舉因異品，兼釋遍無。

The Commentary states: This specifically points out the property. For example, in establishing the thesis 'impermanent', 'being produced' is the reason. If there is a locus that is a collection of permanent properties, it is seen not to be produced, like space and the like; it is called the heterologous class. Since here he is speaking of the heterologous class of the thesis, he should only have said: 'If it is permanent, like space and the like.' That he further says 'it is seen not to be produced' adduces the heterologous class of the reason, concurrently explaining pervasive absence (vipakṣe 'sattva).