def METHOD_NAME(t2, t1a, t1b, fac=1, out=None):
    tmp = einsum('ia,jb->ijab',t1a,t1b)
    t1t1 = tmp - tmp.transpose(1,0,2,3) - tmp.transpose(0,1,3,2) + tmp.transpose(1,0,3,2)
    tau1 = t2 + fac*0.50*t1t1
    return tau1