On the Expressivity of RoCTL*

RoCTL* was proposed to model robustness in concurrent systems. RoCTL* extended CTL* with the addition of Obligatory and Robustly operators, which quantify over failure-free paths and paths with one more failure respectively. Whether RoCTL* is more expressive than CTL* has remained an open problem since the RoCTL* logic was proposed. We use the equivalence of LTL to counter-free automata to show that RoCTL* is expressively equivalent to CTL*; the translation to CTL* provides the first model checking procedure for RoCTL*. However, we show that RoCTL* is relatively succinct as all satisfaction preserving translations into CTL* are non-elementary in length.