<a href="https://en.wikipedia.org/wiki/Barrier_resilience" class="extiw" title="en:Barrier resilience">Barrier resilience</a>: the problem of connecting two designated regions by a path that crosses as few barriers as possible. In this instance there exists a path that crosses only one barrier (the blue one) but it must cross it twice.
<a href="//commons.wikimedia.org/wiki/User:David_Eppstein" class="mw-redirect" title="User:David Eppstein">David Eppstein</a>
<span class="int-own-work" lang="en">Own work</span>