Book excerpt: Information contained in this book is merely for guidance and reference. Due care has been taken to avoid any mistake or omission, the author, the publisher and the printer do not owe any responsibility for any damage or loss to any person on account of error or omission in this publication. Readers are advised to verify the correctness of answers or information from the relevant books on subject. The publishers shall be obliged if mistakes are brought to their notice for corrections in future editions.