All of the given expressions can be considered functions if we interpret them in the right way. Here's how:
1. `x+3=y²` can be written as `y = sqrt(x+3)` (taking the square root of both sides).
2. `x+y=3²` can be written as `y = 9 - x` (subtracting x from both sides).
3. `y=x²-3` is already in the form `y=f(x)`.
4. `y=x+3²` can be written as `y=x+9`.
However, if you consider only the real numbers and not the complex numbers, then the first expression `x+3=y²` is not a function. This is because for certain values of x (specifically x < -3), there is no corresponding real y that would satisfy the equation. So, in the real number system, the first expression would not be a valid function.