5.19 It is known that 1982 people attended a gathering, and among any 4 people, at least 1 person knows the other 3. How many people at least know all the attendees at this gathering?
[Solution] First, let 3 people among 1982, denoted as $A, B, C$, not know each other, while the remaining 1979 people all know everyone present. This scenario clearly meets the requirements of the problem. Therefore, the minimum number of people who know all attendees is no more than 1979.

On the other hand, if the minimum number of people who know all attendees is less than 1979, then at least 4 people do not know everyone. Suppose $A$ and $B$ do not know each other, then apart from $A$ and $B$, there are at least two more people who do not know everyone. Let $C$ not know $D$ and $\{C, D\} \cap \{A, B\} = \varnothing$. In this case, none of the 4 people $A, B, C, D$ know all the other 3, which contradicts the given condition. Therefore, the other two people $C$ and $D$ who do not know everyone must not know at least one of $A$ or $B$. However, this also leads to none of the 4 people $A, B, C, D$ knowing all the other 3, which contradicts the given condition.

In conclusion, at this gathering, the minimum number of people who know all attendees is 1979.