253 Explain the term step-wise refinement. 

Ans:
Step Wise Refinement
Refinement is a process of elaboration. Here one begins with a statement of function
that is defined at a high-level abstraction. That is the statement describes the
program/function conceptually but provides no information about internal working.
Refinement causes the programmer to elaborate on the original statement providing
more and more detail. In a stepwise refinement, at each step of refinement one or
several instructions of the given program are decomposed into more detailed
instructions. The successive refinement terminates when all the instructions are
expressed in terms of atomic expressions of the language.