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Figure 10: Advertising =11<br />

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pattern is explained by the fact that the public platform tends to increase<br />

the socially beneficial advertising.<br />

5.3 Welfare comparisons<br />

In this subsection we compare the social welfare obtained in the three regimes.<br />

First, we compare social welfare in the mixed and the zero duopoly. This<br />

comparison is illustrated in Figure 13, where in region and<br />

in region . According to Figure 13, when advertising is<br />

very harmful the zero duopoly is always better than the conventional mixed<br />

duopoly, from the social welfare point of view. Otherwise, the conventional<br />

mixed duopoly can be socially preferred, as stated in the following proposition.<br />

Proposition 1 In the comparisons between the mixed and zero duopoly, we<br />

obtain that there exists a critical value of k defined as ∗ (), thatisdecreasing<br />

16<br />

18

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