Question

Is (-4,1), (1,8), (-4,-2) a function?

Answer 1

No, the first elements of the pairs are not distinct, yielding two different values for `f(-4)`.

Answer 2

`(x,y)` with `x` mapping into `y` with the set
`color(white)("XXXX")` `{(-4,1), (1,8), (-4,2)}`
is not a function
since `x=-4` maps into more than one value
(it maps into both `1` and `2`).