code: func (mp *TxPool) HaveTransaction(hash *chainhash.Hash) bool {
  	// Protect concurrent access.
  	mp.mtx.RLock()
  	haveTx := mp.haveTransaction(hash)
  	mp.mtx.RUnlock()
  
  	return haveTx
  }
docs: // HaveTransaction returns whether or not the passed transaction already exists
  // in the main pool or in the orphan pool.
  //
  // This function is safe for concurrent access.