Lorentz symmetry is an almost indisputable part of our theories of nature. And an experimentally very well tested part at that. It is nonetheless important to keep testing this symmetry, exactly because we rely so heavily on it in our description of nature. In this student-talk I will try to shine some light on different aspects of Lorentz symmetry: some of its consequences, its connection to CPT, what happens if we break it and how can we test it?

We define the order of a Feynman integral by the number of its denominators (propagators). We then discuss reduction of Feynman integrals at the integrand level at one and two-loop cases. At one-loop level such reductions are known and we just present them with a different approach. At the two-loop level this subject is under investigation since a base for Feynman integrals is not known in advance. However, we explain how one can arrive at such a reduction in a general case.