Department of the Army (1961), Section 5.1. Department of the Army (1961). Army Technical Manual TM 11-684: Principles and Applications of Mathematics for Communications-Electronics.
Baez & Dolan (2001), p. 37 explains the historical development, in "stark contrast" with the set theory presentation: "Apparently, half an apple is easier to understand than a negative apple!" Baez, J.; Dolan, J. (2001). Mathematics Unlimited – 2001 and Beyond. From Finite Sets to Feynman Diagrams. p. 29. arXiv:math.QA/0004133. ISBN3-540-66913-2.
Gschwind & McCluskey (1975), p. 233. Gschwind, Hans W.; McCluskey, E. J. (1975). Design of Digital Computers: An Introduction (2nd ed.). Springer-Verlag.
Textbook constructions are usually not so cavalier with the "lim" symbol; see Burrill (1967), p. 138 for a more careful, drawn-out development of addition with Cauchy sequences. Burrill, Claude (1967). Foundations of Real Numbers. McGraw-Hill. LCCQA248.B95.