Standardization and conservativity of a refined call-by-value lambda-calculus

We study an extension of Plotkin’s call-by-value lambda-calculus via two commutation rules (sigma-reductions). These commutation rules are sufficient to remove harmful call-by-value normal forms from the calculus, so that it enjoys elegant characteriza- tions of many semantic properties. We prove that this extended calculus is a conservative refinement of Plotkin’s one. In particular, the notions of solvability and potential valuability for this calculus coincide with those for Plotkin’s call-by-value lambda-calculus. The proof rests on a standardization theorem proved by generalizing Takahashi’s approach of parallel reductions to our set of reduction rules. The standardization is weak (i.e. redexes are not fully sequentialized) because of overlapping interferences between reductions.