B[a[1,1,2], γa[1,2,4,2,3]//S] - B[a[1,1,2], γa[1,2,4,2,3]]

B[a[1,1,2], γ[-(Subscript[b, 2]),2,3,4]+γa[1,2,3,2,4]] - B[a[1,1,2], γa[1,2,4,2,3]]

B[a[(1/2),1,2], γa[1,2,4,2,3]//S] - B[a[(1/2),1,2], γa[1,2,4,2,3]]

B[a[1,1,2], γ[-(Subscript[b, 2]),2,3,4]+γa[1,2,3,2,4]] - B[a[1,1,2], γa[1,2,4,2,3]//S]