▁L 0 ▁and ▁L 1 ▁have ▁a ▁distant ▁separation ▁D . ▁Let ▁us ▁assume ▁that ▁spac etime ▁is ▁M ink owski . ▁Thus , ▁the ▁minimum ▁time ▁that ▁light ▁takes ▁to ▁travel ▁between ▁L 0 ▁and ▁L 1 ▁is ▁t ▁= ▁D / c , ▁where ▁c ▁is ▁the ▁speed ▁of ▁light ▁through ▁vac u um . ▁A 0 ▁generates ▁a ▁random ▁bit ▁ ▁in ▁a ▁secure ▁labor atory ▁and ▁gives ▁it ▁to ▁B 0 ▁at ▁a ▁time ▁t 0 . ▁B 1 ▁generates ▁a ▁random ▁bit ▁b ▁in ▁a ▁secure ▁labor atory ▁and ▁gives ▁it ▁to ▁A 1 ▁at ▁a ▁time ▁t 1 . ▁B 0 ▁and ▁B 1 ▁communicate ▁ ▁and ▁b ▁through ▁a ▁secure ▁and ▁authentic ated ▁channel . ▁Similarly , ▁A 0 ▁and ▁A 1 ▁communicate ▁ ▁and ▁b ▁through ▁a ▁secure ▁and ▁authentic ated ▁channel . ▁Alice ▁and ▁Bob ▁agree ▁that ▁the ▁output ▁of ▁the ▁toss ▁d ▁is ▁the ▁x or ▁of ▁the ▁bits ▁ ▁and ▁b , ▁. ▁Alice ▁and ▁Bob ▁agree ▁on ▁advance ▁on ▁the ▁values ▁of ▁t 0 ▁and ▁t 1 ▁in ▁a ▁common ▁reference ▁frame , ▁in ▁such ▁a ▁way ▁that ▁| t 0 ▁- ▁t 1 | ▁< ▁t . ▁Thus , ▁from ▁the ▁principle ▁of ▁no ▁super l um inal ▁sign alling , ▁at ▁receiving ▁ ▁from ▁A 0 , ▁B 0 ▁cannot ▁send ▁any ▁signal ▁that ▁arriv es ▁to ▁B 1 ▁before ▁B 1 ▁gives ▁b ▁to ▁A 1 . ▁Therefore , ▁Alice ▁is ▁guaranteed ▁that ▁the ▁bit ▁b ▁is ▁chosen