Read the article "Play around with prices is a bad idea" and answer the following questions:
a) From consumers' point of view, is a negative interest rate bad or good?
b) Assume all your income is spent on two goods: mortgage (in which the price of mortgage is the interest rate) and a composite good (in which its price is $1). With the help of a diagram, explain how a negative interest rate affects your optimal basket of these two goods.