313.0.3. The amount referred to in the first paragraph of section 313.0.1 is the amount by which(a) the aggregate of all amounts each of which is an amount included in the aggregate determined under that paragraph in respect of the acquisition or improvement of a self-contained domestic establishment in which the taxpayer described in the second paragraph of that section 313.0.1 resides, including any payment of principal or interest in respect of a loan made or indebtedness incurred to finance, in any manner whatever, such acquisition or improvement; exceeds
(b) the aggregate of all amounts each of which is an amount equal to 20% of the original principal amount of a loan or indebtedness described in paragraph a.