“…However, Vietoris-Rips ph is notoriously unstable to outliers. Besides other strategies [11,Section 1.7], a commonly proposed remedy for this is the introduction of a second filtration parameter controlling the local density of the point cloud, which leads to the notions of two-and multi-parameter ph [13,42,16,33,40,12]. A central computational problem of two-parameter ph, somewhat akin to the computation of a barcode, is the computation of a minimal free presentation or a minimal free resolution (mfr) of the ph module.…”