When the Wimbledon Tournament is organised, the names of players are drawn from a bag. Each name is then placed in one of two halves of the playing schedule. This sets the order of play and the various contestants in each match.
In this instance, Andy Murray [no. 3 seed] has been placed in the same group as Federer [the upper half] rather than in the group containing Nadal [the lower half].
Since Nadal may well withdraw, it is not really particularly relevant.
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