The poem
Vacuidad ⁄ Forma = Forma ⁄ Vacuidad
The value of emptiness is to the value of form as the value of form is to the value of emptiness.
The middle term repeats
In the ordinary similar triangles poem the four terms are four different things. Here the two inside terms are the same word, and so are the two outside terms. That symmetry has a consequence you can work out on the page: cross-multiplying gives Vacuidad² = Forma², and dividing through gives Vacuidad² ⁄ Forma² = 1.
The two terms are not merely proportional. They are, in the ratio, indistinguishable.