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# Error code E0536

The `not` cfg-predicate was malformed.

Erroneous code example:

    pub fn main() {
        if cfg!(not()) { }
    }

The `not` predicate expects one cfg-pattern. Example:

    pub fn main() {
        if cfg!(not(target_os = "linux")) { } // ok!
    }

For more information about the `cfg` macro, read the section on Conditional Compilation in the Reference.