Mixed dominance game theory I don't quite understand here, how exactly is the strategy $(\sigma_1(U),\sigma(M),\sigma_1(D))=(0,1/2,1/2)$ dominates $U$ since if you look at the first column, $5$ is greates than $3/2+4/2=1.5+2=3.5$ . I'm guessing i'm doing something wrong. Could someone please tell me what i'm doing/thinking wrong?
The text says domination is "in the game remaining after one stage of elimination".

In stage one, column L can be eliminated. As this is exercise b., I am guessing that was exercise a.