[Solved] Let f be a function from a set X to a set Y. Deﬁne precisely (but concisely) what it means for f to be one-to-one. Reinforcement: In behaviorist psychology, any event that strengthens or increases the likelihood of a behavior by providing a consequence an individual finds rewarding. Behavior: Actions or reactions of individuals or groups in response to external or internal stimuli. Single-blind Study: A study or experiment in which the participants do not know which group or condition they have been assigned to, but the researchers do. Experimental Group: Subjects in an experiment who are subjected to the independent variable.