/**
  * returns the fork name for the @argument networkId and @argument blockNumber
  *
  * @param {Object} networkId - network Id (1 for VM, 3 for Ropsten, 4 for Rinkeby, 5 for Goerli)
  * @param {Object} blockNumber - block number
  * @return {String} - fork name (Berlin, Istanbul, ...)
  */
export declare function forkAt(networkId: any, blockNumber: any): any;