In determining the price which unquoted shares or F1unquoted securities might reasonably be expected to fetch if sold in the open market it shall be assumed that in that market there is available to any prospective purchaser of the shares or securities all the information which a prudent prospective purchaser might reasonably require if he were proposing to purchase them from a willing vendor by private treaty and at arm’s length.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F2