With a view to applying the provisions of the articles 39 bis to 39 bis B, the companies concerned are required to attach to each return they submit for income tax purposes a statement showing separately the amount of expenditure incurred for the purposes indicated in the said articles during the period to which the return applies, by deduction, on the one hand, from the profits of the said period and, on the other hand, from the provisions set aside, pursuant to the same articles, from the profits of previous periods.