Abstract
The paper presents another formal proof for the correctness of the Deadline Driven Scheduler (DDS). This proof is different from Zheng Yuhua and Zhou Chaochen's, although both are given in terms of duration calculus (DC) which provides abstraction for random preemption of processor. In the proof of Zheng and Zhou, the induction rules of the duration calculus are heavily applied, but the intuition of the induction propositions is not obvious. However, this proof is to follow and to formalise the original one developed by C.L. Liu and J.W. Layland (1973) which relies on many intuitive facts. Therefore, this proof is more intuitive, while it is still formal.