Definitions for "Indiscernibles"
In mathematical logic, indiscernibles are objects which cannot be distinguished by any property or relation defined by a formula. Usually only first-order formulas are considered. For example, if {A, B, C} is indiscernable, then for each 2-ary formula K, we must have K(A, B) if and only if K(B, A) if and only if K(C, A) if and only if K(A, C) if and only if K(B, C) if and only if K(C, B).