Minimal Projective Resolutions, Möbius Inversion, and Bottleneck Stability

Abstract: We develop a stability theory for minimal projective resolutions of $\mathbf{P}$-modules, where $\mathbf{P}$ is a finite metric poset. On the module side, we introduce the \emph{Galois transport distance}, defined by factoring two modules through a common ``apex'' poset via pairs of Galois insertions and measuring the maximal displacement in the index poset. This construction generalizes the interleaving distance in both the classical one-parameter and multiparameter settings, and yields an extended metric on isomorphism classes of $\mathbf{P}$-modules. On the homological side, we define a bottleneck distance between minimal projective resolutions by matching indecomposable projectives degreewise, with contractible cones playing the role of diagonal terms. Our main theorem shows that this resolution-level bottleneck distance is always bounded above by the Galois transport distance, providing a metric stability result formulated entirely at the level of modules and their minimal projective resolutions. We then treat persistence as an application. Passing to the interval poset and a kernel construction, we interpret persistence diagrams as minimal projective resolutions of kernel modules and obtain a corresponding stability inequality. In the one-parameter case this recovers classical bottleneck stability, while in the multiparameter setting it extends naturally to signed diagrams arising from minimal projective resolutions. Via a general relationship between minimal projective resolutions and Möbius inversion, these results can be interpreted as a stability theorem for Möbius homology, while remaining entirely phrased in the language of projective resolutions.