int on(int ld) {
  pinMode(ld, OUTPUT);
  digitalWrite(ld, 1);
  return 0;
}

int off(int ld) {
  pinMode(ld, OUTPUT);
  digitalWrite(ld, 0);
  return 0;
}

int nt(int ld) {
  int s = digitalRead(13);
  digitalWrite(13, not s);
}

void setup() {
  on(13);
  delay(500);
  off(13);
  delay(500);
  nt(13);
}

void loop() {
  // put your main code here, to run repeatedly:

}