Use of modes. Given the melody and chord symbols for “London Bridge” in Phrygian mode, analyze the chords as lead-sheet symbols (“LSS”) and as Roman numerals (“RN”).
Polychords. Harmonize “London Bridge” using the specified polychords. Remember that the chords can be in any inversion, but should should be playable (i.e., without too big of a stretch for the hands of the pianist).