Injective function
A function f: A → B is said to be one-one if distinct elements in A have distinct images in B.
Example:
Let N be the set of all natural numbers.
Let f: N → N: f(x) = 2x Ɐ x ∈ N
Then, f(x1) = f(x2)
2x1 = 2x2
x1 = x2
Hence, f is one-one.