The book is an abridged version of our work that we carried out in 1998 on the advice and under the able and kind supervision/guidance/support of Prof. A. Z. Butt, Head of the Humanities and Social Sciences Department, Ghulam Ishaq Institute of Engineering Sciences and Technology, Topi. Mr. Mohammad Zubair Khan and Mr. Mohammad Ajmal Khan participated in the work as active members. The work is in many ways courtesy their support and contributions.