ContainsOnly

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ContainsOnly[$list_1$, $list_2$]

yields True if $list_1$ contains only elements that appear in $list_2$.

• • ContainsOnly[{b, a, a}, {a, b, c}]

The first list contains elements not present in the second list:

• • ContainsOnly[{b, a, d}, {a, b, c}]

• • ContainsOnly[{}, {a, b, c}]

Use Equal as the comparison function to have numerical tolerance:

• • ContainsOnly[{a, 1.0}, {1, a, b}, {SameTest -> Equal}]