Howard A. Blair David W. Jakel Robert J. Irwin Angel Rivera Elementary Differential Calculus on Discrete and Hybrid Structures. 41-53 2007 conf/lfcs/2007 LFCS http://dx.doi.org/10.1007/978-3-540-72734-7_4 db/conf/lfcs/lfcs2007.html#BlairJIR07