stanford.edu. 2010-09-01 [2022-06-02]. (原始内容 (PDF)存档于2015-10-09). Ferretti, Elena. The algebraic formulation: Why and how to use it. Curved and Layered
Percy (Acrobatics with dog training) 第14季,2020: Nick Ferretti (30歲的歌手 and guitarist) 第15季,2021: Elena Turcan (10-year-old opera singer) 希腊 Ελλάδα Έχεις