In Exterior Differential Systems, the authors present the results of their ongoing development of a theory of the geometry of differential equations, focusing especially on Lagrangians and Poincare-Cartan forms. They also cover certain aspects of the theory of exterior differential systems, which provides the language and techniques for the entire study, because it plays a central role in uncovering geometric properties of differential equations, the method of equivalence is particularly emphasized. In addition, the authors discuss conformally invariant systems at length, including results on...

Stevie, Carole, and Lisa--founders of The Saddle Club--would do anything to help a friend in need. and now it looks as if they're going to get their chance when Stevie overhears a disturbing conversation between Max, Pine Hollow's owner, and a mysterious caller. Can Stevie believe her ears? Is their riding instructor really in serious financial trouble? Stevie can't be sure, but when Veronica, a snobby girl whose father is president of the local bank, starts looking even more smug than usual, the girls fear the worst. Pine Hollow could be lost! Determined to help bail out Max, the Saddle Club...

The three members of the Saddle Club-Carole, Lisa, and Stevie - are the best of friends, they're together on the long-awaited Mountain Trail Overnight, Riding through the pine forests, swimming in mountain-water ponds, sharing a tent under the stars...