Applications of Groups and Isomorphic Groups to Topics in the Standard Curriculum, Grades 9-11: Part II
Zalman Usiskin · Mathematics Teacher Learning and Teaching PK-12 · 1975
It is possible to form a set in an infinite additive group by beginning with any nonzero real a and adding it to itself over and over again, then including zero and the opposites of all numbers in the set. We call such a set the set of integral multiples of a. If a = 3, then here is such a set.