rule of assignment
a rule of assignment is a subset 
of the broken link: blk:cartesian product 
of two sets, having the property that each element of 
appears as the first coordinate of at most one ordered pair belonging to .
[cite:;taken from @topology_munkres_2014 chapter 1 set theory and logic]
of the broken link: blk:cartesian product of two sets, having the property that each element of appears as the first coordinate of at most one ordered pair belonging to .[cite:;taken from @topology_munkres_2014 chapter 1 set theory and logic]
given a rule of assignment , the domain of is defined to be the subset of consisting of all first coordinates of elements of , and the image set of is defined as the subset of 
consisting of all second coordinates of elements of . formally,
[cite:;taken from @topology_munkres_2014 chapter 1 set theory and logic]
, the domain of is defined to be the subset of consisting of all first coordinates of elements of , and the image set of is defined as the subset of consisting of all second coordinates of elements of . formally,[cite:;taken from @topology_munkres_2014 chapter 1 set theory and logic]