Modify the extract-labels procedure

The following register-machine code is ambiguous, because the label here is defined more than once:

start
  (goto (label here))
here
  (assign a (const 3))
  (goto (label there))
here
  (assign a (const 4))
  (goto (label there))
there

With the simulator as written, what will the contents of register a be when control reaches there? Modify the extract-labels procedure so that the assembler will signal an error if the same label name is used to indicate two different locations.

Nobody's finished this exercise yet. You'll be the first!

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