ABSTRACT
For summants S, T on a figure K we define d ifferential equivalence S ~ T to be J^IS — T\ = 0. This relation is obviously reflexive and symmetric. That is, S ~ S, and S ~ T implies T ~ S. Transitivity follows from the triangle inequal ity, JK \R - T\ < JK \R - S\ + f K \S - T|, which implies R ~ T if both R ~ S and S ~ T.
