I am using Arduino 1.6.9 and cannot get this very basic script to work.    I have TinyScreen+ and GPS module and am just trying to get started.    I finally found and modified a SoftwareSerial module that allowed the sample GPS code to compile but got no output. 

So,  I simplified my code to the bare minimum.   No includes whatsoever. but not output to serial monitor.

Any ideas what is wrong? 
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#define SERIAL_MONITOR Serial


void setup()
{
  SERIAL_MONITOR.begin(115200);
  delay(100);
  SERIAL_MONITOR.print("Attempting to wake GPS module.. ");
  SERIAL_MONITOR.println("done.");
  delay(1000);
} 

void loop() {
  SERIAL_MONITOR.println("next done.");
  delay(1000);
}

I found the answer in a sem-unrelated post.     

Change:
#define SERIAL_MONITOR Serial
To:
#define SERIAL_MONITOR SerialUSB

and it now works.