A vertical line cuts a graph at two points. What does the vertical line test say?

1. A vertical line collects every point of the graph that shares one input value. 2. Two points on that line means one input has produced two different outputs. 3. A function allows only one output per input, so the graph does not define a function. _Source: OpenStax College Algebra (CC BY 4.0), section 3.1 Functions and Function Notation_