(b) the total of each s
uch portion of each amount, if any, by which the cost to the corporation of acquiring a bond, debenture, mortgage, hypothecary claim, no
te or other similar obligation owned by the corporatio
n at the end of the year exceeds the principal amount of the bond, debenture, mortgage, hypothecary claim, note or other similar obligation, as the case may be, at
the time ...[+++] it was so acquired as was deducted by the corporation in computing its profit for the year;