BUILT-IN WOLFRAM LANGUAGE SYMBOL
yields True if no key in the association assoc matches form, and yields False otherwise.
represents an operator form of KeyFreeQ that can be applied to an expression.
Test whether "foo" is a key in the association:
Test whether the association contains a string key:
KeyFreeQ works with lists of rules:
Determine which of the associations does not contain the key:
Introduced in 2015