never {
accept_init:
s1_init:
    if
    :: (r) -> goto s1_init
    :: (p) && (q) && !(r) && (s) -> goto accept_s2
    :: (p) && !(q) && !(r) && (s) -> goto s3
    :: !(s) -> goto s1_init
    :: !(p) && !(r) && (s) -> goto accept_s2
    fi;
s3:
    if
    :: (q) && !(r) -> goto accept_s2
    :: !(q) && !(r) -> goto s3
    fi;
accept_s2:
    if
    :: !(p) && !(r) -> goto accept_s2
    :: (p) && !(q) && !(r) -> goto s3
    :: (r) -> goto s1_init
    :: (p) && (q) && !(r) -> goto accept_s2
    fi;
}