code: def _gamma_trace1(*a):
      gctr = 4  # FIXME specific for d=4
      g = LorentzIndex.metric
      if not a:
          return gctr
      n = len(a)
      if n % 2 == 1:
          # return TensMul.from_data(S.Zero, [], [], [])
          return S.Zero
      if n == 2:
          ind0 = a[0].get_indices()[0]
          ind1 = a[1].get_indices()[0]
          return gctr * g(ind0, ind1)
      if n == 4:
          ind0 = a[0].get_indices()[0]
          ind1 = a[1].get_indices()[0]
          ind2 = a[2].get_indices()[0]
          ind3 = a[3].get_indices()[0]
  
          return gctr * (
              g(ind0, ind1) * g(ind2, ind3)
              - g(ind0, ind2) * g(ind1, ind3)
              + g(ind0, ind3) * g(ind1, ind2)
          )
  
file_path: sympy/sympy/physics/hep/gamma_matrices.py
imports: from sympy.core.mul import Mul
  from sympy.core.singleton import S
  from sympy.matrices.dense import eye
  from sympy.matrices.expressions.trace import trace
  from sympy.tensor.tensor import TensorIndexType, TensorIndex, TensMul, TensAdd, tensor_mul, Tensor, TensorHead, TensorSymmetry
label_desc: Use image node_id 7 for calling a global function with example usage: _gamma_trace1() and returns: gctr, S, unknown, unknown