Properties of Functions
Let S1 = { a, b, c} and S2 = { 1, 2}.
Let f1 = { (a, 1), (b, 1), (c, 2) }
Let f2 = { (a, 1), (b, 1), (b, 2), (c, 1) }
Let f3 = { (a, 1), (b, 2)}
f3 is not a function on S1.
But it is a partial function on S1.
It’s actually a function on { a, b }.