d((x_n),(y_n)) := 2 ^{−min{n∈N: x_n≠y_n}} defines a metric on S={0,1}^ℕ

im currently struggling to prove the statement in the title. I'm aware of how a metric is defined but i have no clue how to prove this. Here is the whole problem, but better readable:

Let S := {0,1}^ℕ the set of 0-1 sequences. Prove that d((x_n),(y_n)) := 2 ^{−min{n∈N: x_n≠y_n}} defines a metric on S.

Found nothing that could help to solve this problem on the internet. I'd be very thankfull for help on this topic

Best regards

 

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