Wasn't sure where to put this, but what is the difference between the symbols and ? I have seen the former a few times, and it seems to be in a similar context to the lattter, but is there actually a difference?
Usually, we can see the two used at the same time in this type of things :
can be written this way :
The is to define the domains, in which range does the domain "maps to"
The is to define by which value a number will be associated. "maps to" too.
All the time I've seen the two, was used for the domain/range and was used for associating a value to a number.
I don't know if you can see the difference with this example... ?