Using given text, extract as many definitions of science fiction

According to Lester del Rey, "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology". According to Robert A. Heinlein, "A handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the nature and significance of the scientific method."