who has coined the concept of in group and out group
Ingroups and outgroups The terminology was made popular by Henri Tajfel and colleagues during his work in formulating social identity theory. The significance of ingroup and outgroup categorization was identified using a method called the minimal group paradigm. Tajfel and colleagues found that people can form self-preferencing ingroups within a matter of minutes and that such groups can form even on the basis of seemingly trivial characteristics, such as preferences for certain paintings.[1][2][3][4][5]
Bracket (mathematics) Historically, other notations, such as the vinculum, were similarly used for grouping; in present-day use, these notations all have specific meanings. The earliest use of brackets to indicate aggregation (i.e. grouping) was suggested in 1608 by Christopher Clavius and in 1629 by Albert Girard.[1]