如果唔用電腦做四色問題，最好既proof係唔係只會證到每個planar graph都可以用五隻色油晒呢?
唔講咁多,自己出個好差既proof挑機 ,有咩柒位就插
For all planar graphs, maximum degree of vertex = 5(唔想proof )
Consider graph g-v(v is the 5-degree vertex),put the 5 neighbours in clockwise order.
Consider v1 and v3:
If v1,v3 are disconnected, we can color them in same color.(done)
Else, we select the subgraph containing v1 and v3. We can color them in 2 colors(color of v1 or v3). if any of v2,v4,v5 are in the subgraph,they will be colored in 1 or 3. (done.)
Else v2 and (v4,v5) are separated. we can color v2 with color 4 or 5(done.)

[#fffcfc]等睇一個formal尐o既 proof [/#fffcfc][/size=2]