> For example, a problem, “what’s the shortest path between two points” Switching to the decision version: "Is there a path of length at most L between the two

> For example, a problem, “what’s the shortest path between two points” Switching to the decision version: "Is there a path of length at most L between the two points?" To verify a "yes" answer, you get a path; and you just verify that it's short enough and goes from the first point to the second; that's it. Obviously this verification doesn't work for a "no" answer.