import { ValidationRule } from './ValidationRule';
export declare const NOT_A_BOOLEAN: 'NOT_A_BOOLEAN';
export declare type NotABoolean = Readonly<{
    type: 'NOT_A_BOOLEAN';
    value: unknown;
}>;
export declare const Booleans: {
    fromBoolean(): ValidationRule<boolean, never, boolean, []>;
    fromUnknown(): ValidationRule<unknown, Readonly<{
        type: "NOT_A_BOOLEAN";
        value: unknown;
    }>, boolean, []>;
};