Dima Grigoriev Nicolai Vorobjov Complexity Lower Bounds for Computation Trees with Elementary Transcendental Function Gates. 185-214 1996 157 Theor. Comput. Sci. 2 db/journals/tcs/tcs157.html#GrigorievV96 http://dx.doi.org/10.1016/0304-3975(95)00159-X