Gumezishn ('Mixture') is the central epoch of Zoroastrian cosmology as narrated in the Bundahishn: the period in which Angra Mainyu invaded Ahura Mazda's originally perfect creation (bundahishn) and commingled evil with good, death with life, darkness with light. The Bundahishn describes this assault in vivid terms — Ahriman piercing the sky, poisoning the waters, withering the primordial plant, slaying the Uniquely-Created Bull (Gav-aevodata). The entire span of cosmic history — the 'limited time' (zaman i kanaragomand) agreed upon by Ohrmazd — is the arena in which this mixture is progressively separated through the righteous acts of humanity, the yazatas, and the Amesha Spentas, culminating in the final Wizarishn (separation) at the Frashokereti.