21-301A Combinatorics
Weeks 8,10,11
Trees
Recall that graph is connected, if for any two vertices x, y, the graph always has a path
from x to y.
Denition. A graph T = (V, E) is a tree, if it is conn
21-301A Combinatorics
Weeks 12-13
Partially ordered set
Let X be a nite set.
Denition. R is called a relation on set X, if R X X.
Here X X := cfw_all ordered pairs (x, y) : x, y X denotes the Cartesi