AbstractGet full access to this articleView all access options for this article.Get accessReferences1. Karlin S. (1969). A first course in stochastic processes. San Diego, CA: Academic Press.2. Slater M. Steed A. (2000). A virtual presence counter. Presence: Teleoperators and Virtual Environments, 9, 413–434. doi:10.1162/105474600566925