stepper_speedControl ( error compilation) RESOLVED

RESOLVED :
in the same windows : GRBL.ino was open

hello,
sketch is original in exemple from this site web .

I don’t understand why it use libraries/grbl/stepper.c.o

/*
 Stepper Motor Control - speed control

 This program drives a unipolar or bipolar stepper motor.
 The motor is attached to digital pins 8 - 11 of the Arduino.
 A potentiometer is connected to analog input 0.

 The motor will rotate in a clockwise direction. The higher the potentiometer value,
 the faster the motor speed. Because setSpeed() sets the delay between steps,
 you may notice the motor is less responsive to changes in the sensor value at
 low speeds.
perso Andre 33 :
Connecter le moteur sur les pins (8 9 10 11)
Il semble que le courant disponible soit trop faible pour permettre le mouvement du chariot;
le moteur fonctionne normalement sans charge. 
cf : https://www.arduino.cc/en/Tutorial/StepperSpeedControl
le circuit ULN2004A est nécessaire avc une alimentation externe 

 Created 30 Nov. 2009
 Modified 28 Oct 2010
 by Tom Igoe

 */

#include <Stepper.h>

const int stepsPerRevolution = 200;  // change this to fit the number of steps per revolution
// for your motor


// initialize the stepper library on pins 8 through 11:
Stepper myStepper(stepsPerRevolution, 8, 9, 10, 11);

int stepCount = 0;  // number of steps the motor has taken

void setup() {
  // nothing to do inside the setup
   Serial.begin(115200);
}

void loop() {
  // read the sensor value:
  int sensorReading = analogRead(A0);
  // map it to a range from 0 to 100:
  int motorSpeed = map(sensorReading, 0, 1023, 0, 100);
  // set the motor speed:
  if (motorSpeed > 0) {
    myStepper.setSpeed(motorSpeed);
    // step 1/100 of a revolution:
    myStepper.step(stepsPerRevolution / 100);
  }
}

error message contents :

HardwareSerial0.cpp.o (symbol from plugin): In function `Serial':
(.text+0x0): multiple definition of `__vector_19'
/var/folders/5j/4mcztk1n40j4fpz02vrkqlww0000gn/T/arduino_build_536971/libraries/grbl/serial.c.o (symbol from plugin):(.text+0x0): first defined here
collect2: error: ld returned 1 exit status
Utilisation de la bibliothèque Stepper version 1.1.3 dans le dossier: /Applications/Arduino 1.8.1.app/Contents/Java/libraries/Stepper 
Utilisation de la bibliothèque grbl prise dans le dossier : /Users/mynameXXX/Documents/Arduino/libraries/grbl (legacy)
exit status 1
Erreur de compilation pour la carte Arduino/Genuino Uno

Thanks

sketch is original in exemple from IDE.

Please post it here so that we can see which sketch you are referring to.

And please post BOTH the error and the code in separate code tags. See How to use the forum.