The loop invariant embodies essential characteristics of loop program and has an important role to play in design, proof and derivation of algorithmicprogram.
循环不变式体现了循环程序的本质特征，在算法程序的开发、证明和推导中具有十分重要的作用。
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Data refinement is hard to deal with in a refinement tool compared with ordinary algorithmic refinement, since data refinement usually has to be done on a large program component at once.