 Note that formula_87 itself can be considered as a stack, the moduli stack of principal "G"-bundles on "X".An important subexample from this construction is formula_91 which is the moduli stack of principal formula_92-bundles.Since the data of a principal formula_92-bundle is equivalent to the data of a rank formula_94 vector bundle, this is isomorphic to the moduli stack of rank formula_94 vector bundles formula_96.