1, surjective: for any b, there is a that satisfies f(a) = b, that is, the interval y is full, and each y has an x correspondence, and there is no case where a y has no x correspondence.
2. injectivity: (one-to-one function) one-to-one function, different X, different Y. That is, no X corresponds to two Y's and no Y corresponds to two X's.
Conceptual explanation
If every possible image has at least one variable mapped on it, or any element in the range has at least one variable corresponding to it, then this mapping is called surjection.
Let F be the mapping from set A to set B. If X, y∈A and x≠y all have f(x)≠f(y), then F is called injectivity from A to B. The mapping that is both injective and surjective is called bijection, which is also called "one-to-one mapping".
In mathematics, injective function is a function that connects different independent variables and different values. More precisely, when the function f is said to be injective, there is at most one x in the definition domain for y in each value domain, so that f (x) = y.