if (!is_a<spinidx>(i1) || !is_a<spinidx>(i2))
throw(std::invalid_argument("indices of spinor metric must be of type spinidx"));
if (!ex_to<idx>(i1).get_dim().is_equal(2) || !ex_to<idx>(i2).get_dim().is_equal(2))
throw(std::runtime_error("index dimension for spinor metric must be 2"));
if (!is_a<spinidx>(i1) || !is_a<spinidx>(i2))
throw(std::invalid_argument("indices of spinor metric must be of type spinidx"));
if (!ex_to<idx>(i1).get_dim().is_equal(2) || !ex_to<idx>(i2).get_dim().is_equal(2))
throw(std::runtime_error("index dimension for spinor metric must be 2"));