The slushy history of the Slurpee: Can Dallas claim the icy treat?

FROM WFAA: 

Dallas has at least one icy concoction on its résumé.

When Mariano Martinez wanted to improve the consistency of the margaritas at his East Dallas Tex-Mex restaurant in the early 1970s, he converted a soft-serve ice cream dispenser into the world’s first frozen margarita machine.

But can Dallas also claim the frozen concoction that supposedly inspired Martinez’s innovation?

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