Discussion:
Q: Describe each of the following as an indexed family of sets. Here, pi denotes the coordinated xy-plane.
a) The family of closed intervals of length 1 on the real line.
b) The family of all circles in pi of radius 1 whose center is on the y-axis.
c) The family of all circles in pi of radius 1.
d) The family of all lines in pi with slope 6.