Similar to the problems of defining literature and film, no consensus has been reached on a definition of the comics medium, and attempted definitions and descriptions have fallen prey to numerous exceptions. Theorists such as Töpffer, R. C. Harvey, Will Eisner, David Carrier, Alain Rey, and Lawrence Grove emphasize the combination of text and images, though there are prominent examples of pantomime comics throughout its history. Other critics, such as Thierry Groensteen and Scott McCloud, have emphasized the primacy of sequences of images. Towards the close of the 20th century, different cultures' discoveries of each other's comics traditions, the rediscovery of forgotten early comics forms, and the rise of new forms made defining comics a more complicated task.