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I agree with you that Barcelona cannot catch up with Real Madrid at the top of the La Liga table. Real Madrid is leading Barcelona with 8 points, and it will be hard to drop points that will make Barcelona equal or overtake them at the top of the La Liga table.
Difficult doesn't mean impossible, meaning that as long as Real Madrid can't guarantee the title mathematically, Barcelona and Girona still have a chance to win the title this season. Being 8 points ahead of Barcelona clearly makes Real Madrid very comfortable at the top of the standings without too much interference, but every time they lose points it will increase the pressure.
So far I don't think Real Madrid can win all the games for the rest of the season, meaning they still have the chance to lose points regardless of how low or high the odds they get from the betting books. There are several difficult matches waiting for Real Madrid in the remainder of the season, so I am not completely sure they can secure 3 points in every match.