The Combination of Wilson Loops into $J^{PC}$ Operators in Lattice Pure   Gauge Theory
  To calculate the mass of glueballs with quantum number $J^{PC}$ in lattice gauge theory by using Wilson loops, we discuss their combinations of Wilson loops into irreducible representation of $O^{PC}$ group for arbitry-link wilson loops. We present a general computational procedure for this combination which is suitable for any finite groups. 
Da Qing Liu, Ji Ming Wu and Ying Chen