The goal of this paper is to cross-linguistically examine the equivalence between a single heavy-syllable foot and a two-light syllable foot in the rhythmic grouping. In spite of their bimoraicity nature in quantity, (μμ)F=(μμ)F does not function equally across languages under the guidance of quantitative asymmetry between iambs and trochees proposed by Hayes (1995).
In iambic system languages the iambic-specific phonological process such as Iambic Lengthening attempts to be the best quantitative shapes of disyllabic uneven iambs (LH) by means of lengthening the strong branch of (LL). As a result, the rank of (H) > (LL) comes out. The Trochaic Shortening process does the same role in the trochaic system languages to reach the harmonic goal of disyllabic even trochee (LL), producing (LL) > (H), otherwise (LL) and (H) are not scaled each other.
Therefore, the equivalence between (μμ)F and (μμ)F does not seem to be a universal principle but a strong linguistic tendency which is varied with the presence of language-specific phonological processes like Iambic Lengthening and Trochaic shortening and their hierarchical constraint rankings wiith other constraints.