Leray's theorem
In algebraic topology and algebraic geometry, Leray's theorem (so named after Jean Leray) relates abstract sheaf cohomology with Čech cohomology. Let   be a sheaf on a topological space  and   an open cover of  If   is acyclic on every finite intersection of elements of  , then   

where   is the -th Čech cohomology group of   with respect to the open cover

References 
 Bonavero, Laurent. Cohomology of Line Bundles on Toric Varieties, Vanishing Theorems. Lectures 16-17 from "Summer School 2000: Geometry of Toric Varieties." Sheaf theory
Theorems in algebraic geometry
Theorems in algebraic topology