Do I have a prime twin?
Brachylog, 9 8 bytes
ṗ∧4√;?+ṗ

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Explanation
ṗ           Input is prime
 ∧          And
  4√        A number whose square is 4 (i.e. -2 or 2)
    ;?+     That number + the Input…
       ṗ    …is prime