A i σ i e i δ ai satisfying the following σ i e δ

( A
i
) , σ
i
∶ E
i
→
Δ ( A
i
) satisfying the following:
σ
i
( e ) ∈ Δ ( A ( e )) .
25

Theorem 2 (Kuhn (1953)) Every mixed strategy is equivalent to the unique
behavior strategy it generates and each behavior strategy is equivalent to
every mixed strategy that generates it.
26

Beliefs
Let ν
i
denote the nodes controlled by player i :
ν
i
= { n ∈ ν ∶ ı ( n ) = i } .
A belief for player i is a mapping β
i
∶ E
i
→ ν
i
from each e ∈ E
i
into Δ ( ν
i
)
satisfying the following:
β
i
( e ) ∈ Δ ( e ) .
(This is just requiring that beliefs respect the structure of E
i
, which is as-
sumed to be common knowledge between the players.)
Beliefs represent the players’ subjective probability of being at any given
node, conditional on an information set.
27

Normal (or Strategic) Form Games
A matrix-based representation of games.
28

Player 2
Player 1
A (4X3) Normal Form Game
L C R
a
b
c
d
1, 5
3,10
-3,2
4,0
2,-1
5,3
2,2
7,3
6,5
2,-4
-4,-2
0,7
29

Player 2
Player 1
A (2X2X3) Normal Form Game
L R
x
y
1,5,6
3,0,10
2,-1,3
5,3,4
Player 3 plays T
Player 2
Player 1
L R
x
y
3,5,5
13,1,0
4,5,1
8,1,3
Player 3 plays M
Player 2
Player 1
L R
x
y
2,1,5
0,6,-2
5,2,-1
8,5,3
Player 3 plays B
30

Player 1
Player 2
Player 2
Normal Form Representation of Extensive Form
L R
(a,a)
(a,b)
(b,a)
(b,b)
1, 5
-3,2
1, 5
-3,2
2,-1
2,-1
5,3
5,3
L R
a b a b
Player 1
1,5 -3,2 2,-1 5,3
31

Player 1
Player 2
Player 2
Normal Form Representation of Extensive Form
L R
a
b
1, 5
-3,2
2,-1
5,3
L R
a b a b
Player 1
1,5 -3,2 2,-1 5,3
32