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clefs 
Signs placed at the beginning of the staff and named after the note they refer to.
C clef
Rarely used clef indicating that the line chosen (first, third or fourth) corresponds to the note C; its use is more specialized.
F clef
Key indicating that the fourth line of the staff corresponds to the note F; it is used to write notes in the middle and bass registers.
G clef
Key indicating that the second line of the staff corresponds to the note G; it is used to write notes in the middle and treble registers.
