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The sequences allowed are hence a.b.c,b.a.c and b.c.a, interleaving the action a of the left process with b and later c of the right process.
允许的顺序因此是a.b.c,b.a.c 和b.c.a,这里面交叉着b的左移动作和稍后的c的右移动作.
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这里的left process 可能要看上下文
