雙向圖(ambigram,或叫inversion、 flipscript)不只是把字語對換的形式,而是從不同方向也可以閱讀、圖形式的文字。雙向圖可以是一些字組成的,方向不同、字相同型式的雙向圖比較多,不過也有方向不同、字也不同型式的雙向圖。美國學者侯世達(Douglas Richard Hofstadter)也把雙向圖描述為「把兩種不同讀法字擠進同一個曲線的的筆記體設計」(calligraphic design that manages to squeeze two different readings into the selfsame set of curves.)。
Hofstadter, Douglas R., "Metafont, Metamathematics, and Metaphysics: Comments on Donald Knuth's Article 'The Concept of a Meta-Font'" Scientific American (August 1982) (republished in the book Metamagical Themas)
Langdon, John, Wordplay: Ambigrams and Reflections on the Art of Ambigrams, Harcourt Brace (1992, republished 2005)
Hofstadter, Douglas R., Ambigrammi, Hopefulmonster Editore Firenze (1987) (in Italian)
Polster, Burkard, Les Ambigrammes l'art de symétriser les mots, Editions Ecritextes (2003) (in French)