Please add spaces between words: Thethirdlecturegivestheessentialstepsintheenumerationoftheseventeenspace-groupsoftwo-dimensionalcrystallography...[Inthefourthlecturehe]showshowthespecialtheoryofrelativityisessentiallythestudyoftheinherentsymmetryofthefour-dimensionalspace-timecontinuum,wherethesymmetryoperationsaretheLorentztransformations;andhowthesymmetryoperationsofanatom,accordingtoquantummechanics,includethepermutationsofitsperipheralelectrons.
The third lecture gives the essential steps in the enumeration of the seventeen space-groups of two-dimensional crystallography ... [In the fourth lecture he] shows how the special theory of relativity is essentially the study of the inherent symmetry of the four-dimensional space-time continuum, where the symmetry operations are the Lorentz transformations; and how the symmetry operations of an atom, according to quantum mechanics, include the permutations of its peripheral electrons.