2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/101475The quantum adversary method is one of the most versatile lower-bound methods for quantum algorithms. We show that all known variants of this method are equivalent: spectral adversary (Barnum, Saks, and Szegedy, 2003), weighted adversary (Ambainis, 2003), strong weighted adversary (Zhang, 2005), and the Kolmogorov complexity adversary (Laplante and Magniez, 2004). We also pa few new equivalent formulations of the method. This shows that there is essentially _one_ quantum adversary method. From our approach, all known limitations of these versions of the quantum adversary method easily follow.18 pages, ICALP 2005, LNCS 3580, v2: polished and fixed one proof, v3: generalized the adversary bound to non-Boolean functions and published in ToCQuantum Physicstext