William and Jill Hunter (defendants) rented an apartment from Stephen Wolfberg (plaintiff). In September 1978, the Hunters told Wolfberg that their apartment had mice. The problem continued for five months. In November 1978, the Hunters told Wolfberg they would not pay rent until the mice were gone. The Hunters did not pay rent for three months. Wolfberg sued the Hunters to recover the unpaid rent. The Hunters sued Wolfberg for breach of the implied warranty of habitability. The trial court ruled in favor of the Hunters. The trial court initially calculated the Hunters’ damages as: (1) the agreed rent for a rodent-free apartment over the five months, minus (2) what the rent should have been during those five months for a mouse-infested apartment, plus (3) the Hunters’ costs to fix the problem. Wolfberg did not challenge this formula, but Wolfberg did ask the trial court to prevent the Hunters from recovering damages for the three months they withheld rent. Wolfberg’s calculation would only look at the two months in which the Hunters both had mice and paid rent. The trial court agreed that the Hunters should not get any damages for the three months they withheld rent. Both parties appealed.