The following excerpt is taken from an article titled “Denver Investment to Make $800 Million Treasury Move,” that appeared in the December 9, 1991, issue of BondWeek, p. 1:
“Denver Investment Advisors will swap $800 million of long zero-coupon Treasuries for intermediate Treasuries... . The move would shorten the duration of its $2.5 billion fixed-income portfolio.. . .”
Why would the swap described here shorten the duration of the portfolio?