listing of securities

For a company to get listed, various conditions and comittments are required to be met. Different stock exchanges demand different committments to be fulfilled. Shareholdings / Minimum number of shareholders for listing is one among them. The numbers vary for listing purposes, continuous listing and also for different for bringing the open offer for purchase. My specific question is what is the minimum number of shareholders that are required for a. Listing b. Continuous listing c. Bringing up open offer for the companies listed on Calcutta stock Exchange... It would also be worthy if the criteria on which such numbers are decided is brought to notice Pls substantiate your answers with a valid source.(links or references may be attached with the posts) Rupal Aasat