Upward confluence in the interaction calculus

Abstract: The lambda calculus is not upward confluent, one of counterexamples known thanks to Plotkin. This paper investigates upward confluence in the interaction calculus. Can an interaction system have this property? We positively answer this question and also provide a necessary and sufficient condition for stronger one-step upward confluence which happens to be very restrictive. However, the provided condition is not necessary for upward confluence as we prove that the interaction system of the linear lambda calculus is upward confluent.