DuplicateFreeQ

DuplicateFreeQ[list] gives True if list has no duplicates, and False otherwise.

DuplicateFreeQ[list,test] applies test to pairs of elements to determine whether they should be considered duplicates.

Examples

Check if a list has no duplicates:

DuplicateFreeQ[{a, b, c}]
(* True *)

DuplicateFreeQ[{a, b, a}]
(* False *)

Please visit the official Wolfram Language Reference for more details.