code: def overlap1d(l1,l2,PAx,PBx,gamma):
      
      total = 0
      for i in range(1+int(floor(0.5*(l1+l2)))):
          total += binomial_prefactor(2*i,l1,l2,PAx,PBx)* \
                   fact2(2*i-1)/pow(2*gamma,i)
      return total
docs: The one-dimensional component of the overlap integral. Taken from THO eq. 2.12
      >>> isclose(overlap1d(0,0,0,0,1),1.0)
      True