In 1972, the taxpayer and other employees of a private company were offered convertible debentures of their employer which, in the case of the taxpayer, had a principal amount of $5,000. When in 1977 the taxpayer exercised the conversion rights under his debenture to acquire shares of his employer with a fair market value of $11,700, he was deemed by s. 7(1)(a) to receive a taxable benefit equal to the difference between such fair market value and the $5,125 price for which his convertible debenture had been issued to him. This benefit was not exempted from taxation by s.