Function
Function: A binary relation whose first components are from a set called the domain, and whose second components are from a set called the range, and such that each domain element is paired with one and only one range element.
D = {a, b, c}; R = {0, 1}
F = { (a,0), (b,0), (c,1)} is a function from D to R.
B = { (a,0), (a,1), (b,0), (c,0) } is not a function.