A characterization of 2-fold torsion classes induced by $\tau$-rigid modules

We introduce $n$-fold torsion(-free) classes of an abelian category. These are a generalization of ordinary torsion(-free) classes in the sense that $1$-fold torsion(-free) classes coincide with torsion(-free) classes. In the category of finitely generated modules over a finite dimensional algebra, we can naturally construct $n$-fold torsion classes from $\tau$-rigid modules. We characterize the $2$-fold torsion classes induced by $\tau$-rigid modules.