 In the early 1980s, Irene Heim (1982) and Hans Kamp (1981) independently formulated very similar semantic theories that were in part designed to handle problematic anaphora, particularly donkey and discourse anaphora. The theories developed by Heim and Kamp have come to be known as Discourse Representation Theory or DRT (see entry on  Discourse Representation Theory).[10]  We shall not attempt to describe differences between the formulations of Heim and Kamp. Indeed, in our exposition we shall combine elements of the two theories. Readers interested in the differences between the two accounts should consult Heim (1982) and Kamp (1981) directly.