Letters to the Editor

Thus far, I believe, describing various approximately 120 copies have been limitations of QSIM. At the risk of distributed. The QSIM program is a being scolded again for "employing research tool, not a product, so any universal truths and unarguable commercial rights are retained, and I facts" in support of my position, I cannot warrant that it is free of bugs. Hall examination of the limitations of University of Texas at Austin one's own work is an invaluable Austin, Texas 78712 guide to further research. Akman observes, correctly, that References QSIM is a purely mathematical formalism for expressing qualitative differential Crawford, J.M., Farquhar, A., and Kuipers, 8. 1590 QPC: A Compiler from equation models of the Phvsical Models into Qualitative Differential world, and not a physical modeling Equations In Pr&eedings of the Thank you for publishing our reply Akman's letter refers to his difficulties to Prof. Kuipers in the last issue.