import type { PropFormula } from "../../models";
/**
 * Checks if negation introduction is applicable.
 *
 * Negation introduction allows us to infer ¬A from two implications:
 *  1) A → B
 *  2) A → ¬B
 *
 * @param formulas - An array of propositional formulas to check.
 * @returns `true` if we can infer negation, otherwise `false`.
 * @category Validators
 */
export declare function isNegationIntroductionApplicable(formulas: PropFormula[]): boolean;