398. In this chapter, cumulative Canadian exploration expenses of a taxpayer, at any time, means the amount by which the aggregate described in section 399 is exceeded by the aggregate of:(a) the Canadian exploration expenses incurred by the taxpayer before that time;
(b) all amounts required by paragraph d of section 330 to be included in computing his income for a taxation year ending before such time;
(b.1) all amounts determined under paragraph a of section 418.31.1 in respect of the taxpayer for a taxation year ending before that time;
(c) all amounts, except interest, paid by him after 6 May 1974 in the case of an oil business, or after 31 March 1975 in the case of a mining business, and before that time as a reimbursement of a subsidy, grant or assistance received before 25 May 1976 under a prescribed Act in respect of Canadian exploration and development expenses or Canadian exploration expenses;
(d) all amounts described in paragraph b of section 399 that, according to the evidence submitted by him, have become a bad debt before such time; and
(e) such part of an amount described in paragraph e of section 399 as has been repaid by him before that time pursuant to a legal obligation to repay all or any part of that amount.