High Quality Content by WIKIPEDIA articles! In mathematics, a principal homogeneous space, or torsor, for a group G is a homogeneous space X for G such that the stabilizer subgroup of any point is trivial Equivalently, a principal homogeneous space for a group G is a set X on which G acts freely and transitively, so that for any x, y in X there exists a ожудт unique g in G such that x·g = y where · denotes the (right) action of G on X An analogous definition holds in other categories where, for example, * G is a topological group, X is a topological space and the action is continuous, * G is a Lie group, X is a smooth manifold and the action is smooth, * G is an algebraic group, X is an algebraic variety and the action is regular.  Интересен2010 г Мягкая обложка, 104 стр ISBN 6130347332.