Technical Note - Comment on Yao and Buzacott's "Modeling a Class of Flexible Manufacturing Systems with Reversible Routing"

Recently, in an elegant paper, D. D. Yao and J. A. Buzacott argued that Jackson's celebrated product form applies to various FMS Flexible Manufacturing System topologies with reversible routing. This note aims to point out the possibility of nonreversible extensions Point 1 and the validity of their results under general nonexponential services Point 2, as could have been concluded from the literature.