Tylko jedno w głowie mam
koksu pięć gram
odlecieć sam
w krainę za zapomnienia

you need to give us more information since we can't answer

sample answer: you can determine whether each element of the domain is paired with exactly one element of the range. for example, if given a graph, you could use the vertical line test; if a vertical line intersects the graph more than once, then the relation that the graph represents is not a function.