[5]

在一张长方形的桌面上放了n个一样大小滴硬币。这些硬币中可能有一些不完全在桌面内，也可能有一些彼此重叠；当再多放一个硬币而它的在桌面内时，新放的硬币便必定与原先某些硬币重叠。

1- from known - all points on table must be less than 2R away from at least one given 圆心;

2- Let's make all coins twice larger (R->2R).

3- based on 1- this table should be completly covered by n enlarged coins.

4- Duplicate the layout in step 3 to four tables and 4n enlarged coins

5- I can prove 4 tables are completly covered with 4n enlarged coins.

6- Now I reduce everything by 100% - so I have ONE regular table coverd with 4n REGULAR coins.