anchor.diff:  They have no line number.
   They are available only in "run" mode.
   
  -NEW
  -~~~
  -
  -Clears the current program.
  -Does not ask to save a loaded program.
  -
  -Syntax:	NEW
  -
  -LOAD
  -~~~~
  -
  -Loads a stored program into memory.
  -Sorts statements by line number.
  -Clears the current program prior to loading the new one.
  -
  -Syntax:	LOAD filename
  +CROSSREF
  +~~~~~~~~
  +
  +Lists the numeric constants, text constants, functions, and variables used in the program, along with the line numbers on which they appear.
  +
  +DELETE
  +~~~~~~
  +
  +Removes lines from the program.
  +
  +My experience with other BASIC interpreters is that lines can be deleted by simply typing a line number and pressing RETURN.
  +(That is, entering an "empty" line with line number and nothing else.)
  +That technique does not work with BASIC-1973, as BASIC-1973 allows empty lines to be part of a program.
  +
  +So how to remove a line from a program?
  +Replacing a line with an empty line is possible, and certainly makes the offending line "go away" from execution, but what if we want to really remove a line?
  +
  +That's what the DELETE command does.
  +
  +DELETE uses the same specification as the LIST command.
  +
  +Syntax:	DELETE [line specification]
  +
  +If the list specification is a single line, it is deleted immediately.
  +If the list specification is a range, the lines are displayed and the user must confirm the operation.
  +
  +The DELETE command with no specification (implying the entire program) does not delete the program but does nothing.
  +(To delete the entire program, use the NEW command.)
   
   LIST
   ~~~~
  
positive.code: These lines are processed before the program begins, and they do nothing when executed in the main execution.
  For example, placing a DATA statement inside of a FOR/NEXT loop does not cause the lines data values to be stored multiple times.
  
  DELETE
  ~~~~~~
  
  Removes lines from the program.
  
  My experience with other BASIC interpreters is that lines can be deleted by simply typing a line number and pressing RETURN.
  (That is, entering an "empty" line with line number and nothing else.)
  That technique does not work with BASIC-1973, as BASIC-1973 allows empty lines to be part of a program.
  
  So how to remove a line from a program?
  Replacing a line with an empty line is possible, and certainly makes the offending line "go away" from execution, but what if we want to really remove a line?
  
  That's what the DELETE command does.
  
  DELETE uses the same specification as the LIST command.
  
  Syntax:	DELETE [line specification]
  
  If the list specification is a single line, it is deleted immediately.
  If the list specification is a range, the lines are displayed and the user must confirm the operation.
  
  The DELETE command with no specification (implying the entire program) does not delete the program but does nothing.
  (To delete the entire program, use the NEW command.)
  
  RENUMBER
  ~~~~~~~~
  
  
negative.code: Syntax:	PRETTY [line specification]
  
  The line specification is the same as the line specification for the LIST command.
  
  PROFILE
  ~~~~~~~
  