I could use >= to for one side of the arguments to include those values, but I don't really think it's needed.
How do you think you will get working/robust/failsafe programs if you "deny" simple bugs like this one. There are zillion projects (including my own) that tried hard to make programs robust and still unwanted sideeffects (aka bugs) appeared. Read History's Worst Software Bugs History's Worst Software Bugs | WIRED
For those with a deeper interest in bugfree software development - not available for Arduino 
http://www.verum.com/pdf/resources/locked/White_Paper_An_Introduction_to_ASD.pdf
"there are so many errors to choose from, so why make them twice"