IF FILE("myfile.chk")

  lnTemp = FOPEN("myfile.chk")

  IF lnTemp < 0

    ** If here, another instance has this file locked, so the
    ** application is already running

  ELSE
  
    ** If here, no other instance is running, so store the file
    ** handle for later use
    PUBLIC gnHandle
    gnHandle = lnTemp

  ENDIF

ELSE

  ** No other instance is running
  PUBLIC gnHandle
  gnHandle = FCREATE("myfile.chk")

ENDIF