[[!meta copyright="Copyright © 2007, 2008 Free Software Foundation, Inc."]] [[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable id="license" text="Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled [[GNU Free Documentation License|/fdl]]."]]"""]] When two [[principal]]s cannot affect each other, they are said to be isolated from one another. Strictly speaking, if two principals are isolated from one another, there is no way for one to know whether the other exists: all interactions with the environment do not expose proof of the existence or non-existence of the other. Typically, principals are isolated from one another with respect to a particular property. Common properties include information-flow (security) and performance.