Warning: Variable xv only occurs once in file circuit_records.dl at line 76
    l = [[x,xv],tail].
------------^----------
Warning: Variable tail only occurs once in file circuit_records.dl at line 76
    l = [[x,xv],tail].
----------------^------
Warning: Variable xv only occurs once in file circuit_records.dl at line 82
    l = [[x,xv],tail],
------------^----------
Warning: Variable tail only occurs once in file circuit_records.dl at line 82
    l = [[x,xv],tail],
----------------^------
