Yosida frames in free abelian ℓ-groups

We prove that for any finitely generated projective abelian ℓ-group G, whence for any finitely generated free abelian ℓ-group, the lattice of ℓ-ideals of G is a Yosida frame. This answers a problem posed by Martínez and Zenk (2006) in their paper [12].