verification is the process of proving or demonstrating 
that the program correctly satisfies the specifications. 
“each step of the development process correctly echoes the 
intentions of the immediately preceding step.”

Validation: Validation is the process of evaluating 
software, at the end of the development process, to ensure 
compliance with requirements.
 that the verification community also uses the term 
validation to differentiate formal functional verification 
from extensive testing of a program against its 
specifications