import type { IFunction } from '@stoplight/spectral-core';
/**
 * Checks if each abstract declaration in the model has at least one concrete subclass.
 *
 * Iterates through the model's declarations, collects all abstract types,
 * and removes any abstract type that is extended by a concrete subclass.
 * Returns a result for each abstract type without a concrete subclass.
 *
 * @param {unknown} targetVal The AST model object containing declarations.
 * @returns {IFunctionResult[] | void} An array of results for abstract declarations lacking concrete subclasses.
 * @throws {Error} If the input is not a valid model AST.
 */
export declare const hasConcreteSubclass: IFunction;