Graph Editor
Click empty space: add node
Click node: select
Click 2 nodes: add/remove edge
Right-click node: delete
k=3
Chromatic Polynomial P(k):
—
P(k) = # proper k-colorings
Deletion-contraction: P(G,k) = P(G−e,k) − P(G/e,k)
Base: P(Kₙ,k) = k(k−1)…(k−n+1)
Chromatic number χ(G) = smallest k with P(k)>0.
P(k) is a polynomial with alternating signs; leading term = k^n.