11 21

a b c e f g h i j s t 

s a 1 
s b 1 
s c 1

a b 1 
a e 1 
a f 1 

b f 1 

c g 1 

e f 1 
e h 1 
e i 1 

f i 1 
f g 1 
f j 1 

g j 1 
g b 1 

h t 1 

i h 1
i t 1 
i j 1 

j t 1 


s t