Carrying out on Shabbat - two that are four

The Mishnah builds four cases for each side: who lifted the object and who set it down. The principle: liability for carrying requires lifting from one domain and placing in another by the same person. When lifting and placing are split between two people, both are exempt from a sin-offering, though the Sages prohibited it.

1. 1Restate the source in your own words.
2. 2Identify the central distinction and explain its significance.
3. 3Apply the distinction in the exercise without adding a ruling absent from the source.