1. For every pair of real numbers x, y; √(x+y) = √x + √y
2. There exists a real number x such that x² < x

3. Every real number is an integer

4. There exists a natural number x such that x² = 2
5. ∃ x ∈ R s.t. ∀ y ∈ R s.t. x + y = y

Choose all that are injective (1-1), (write in ascending order: 1, 2 ...etc)

1.     f(x) = 7x + 2 , R → R
2.     f(x) = x³ - 4x , R → R
3.     f(x) = x + 1 , N → N

S is the relation defined on Z (all integers) as follows: 

For every m, n ∈ Z, relation m S n states: m − n is odd.