Blinker environment setting /DI3
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 Setting /DI3 (DEBUG INT 3) in the BLINKER environment variable causes a
 debug interrupt 3 to be created just before the far jump to the first byte
 of the actual program. This is after both the extender and the Blinker
 Kernel have loaded and initialised. This instruction can be stepped into in
 the normal way to take you to the first byte of the actual program.

 In high level language programs this will be the library start up code, so
 to skip over the library start up to the start of your program (function
 MAIN) type 'G MAIN' or its equivalent.