ScrollViewSchool Pt13 UIPageViewController Min(Max?

I was able to update the Scroll School tutorial for Part 13 to Swift 3 & got it to run. Anyone looking for a working copy, I’ve posted mine on GitHub:
https://github.com/gallaugher/Swift3ScrollSchoolPart13

There’s one bit that I don’t understand. In the file PagedViewController.swift, the function below:

func tutorialStepForPage(_ inPage: Int) -> TutorialStepViewController {
let tutorialStep = storyboard!.instantiateViewController(withIdentifier: “TutorialStepViewController”) as! TutorialStepViewController
let page = min(max(0, inPage), pageCount-1)
tutorialStep.page = page

if inPage is passed, why can’t we simply:
let page = inPage
meaning, why do we need:
let page = min(max(0, inPage), pageCount-1)

Thanks for helping me understand this!
John