(Continuation of the Mishnah): If he found it (even) in (an open) shed, he is not responsible for it' if he found in a public place, he is responsible for it.

If it was between graves, he should not become impure for it (if he is a Kohen).

If his father told him to become impure or his father told him not to return it, he should not listen to him.

If he unloaded and reloaded, unloaded and reloaded, even four or five times, he must still continue, as the pasuk states (Shemos 23, 5), "azov ta'azov - you shall surely help him'' (even multiple times).

If the owner went and sat down and said to him, "Since it is your Mitzvah (to help me), if you wish to unload it, unload it!'' - he is exempt, as the pasuk states, "...with him''.

If the owner was sick or elderly, he must help him.

It is a Biblical Mitzvah to help him to unload but not to load.

R. Shimon: Even to load.

R. Yosi Haglili: If it was overloaded, he is not required to reload it, as the pasuk states (ibid), "under its load'' - meaning a load that it is able to bear.

(Gemara- question): Usually we say that a positive Mitzvah overrides a negative Mitzvah; but here the negative overrides the positive?! (As the negative Mitzvah to ignore a lost item overrides the positive Miztvah to honor one's father.)

Answer: Here is different because both he and his father are obligated to honor Hash-m.