code: func (mp *TxPool) haveTransaction(hash *chainhash.Hash) bool {
  	return mp.isTransactionInPool(hash) || mp.isOrphanInPool(hash)
  }
docs: // haveTransaction returns whether or not the passed transaction already exists
  // in the main pool or in the orphan pool.
  //
  // This function MUST be called with the mempool lock held (for reads).