R Zarei - School of Mathermatical Sciences , Isfahan University of Technology
SM Taheri - School of Mathermatical Sciences , Isfahan University of Technology

The extension principle is generalized for vague sets . An especial kind of vague sets . Called vague numbers , is introduced . Using the generalizd extension principle . The arithmetic operation with vague numbers are defined and investigated . Suggested concepts are illustrated by numerical examples.

Extension Principle, Vague set , Vague number