It's always happy at the banana stand
- Sheng is happy today only if Tracy and Jamal were both happy yesterday.
- Jamal is happy today only if Sandip or Sheng (or both) were happy yesterday.
- Sandip enjoys watching Sheng cry, so Sandip is happy today only if Sheng was sad yesterday.
- Tracy is happy today only if Tracy was happy yesterday, meaning she has an independent streak.
Suppose that on day 1, all four of the friends are sad. After a few days, the friends reach a stable emotional state that repeats itself. What is the emotional state of each person in this repeating state?