  We consider properties of connected diagrams with fermion-photon interaction
and such fermion and photon propagators and vertex function that the values of
these diagrams are finite. We establish the properties of these propagators and
vertex function that imply that these diagrams are invariant under C, P, T, CP,
CT, PT, or CPT transformations up to some phase factor common to each process.
We introduce eight new transformations related to Hermiticity and establish the
conditions under which they leave the tree transition probabilities invariant.
We determine such general Lorentz form-invariant fermion and photon propagators
and fermion-photon vertex functions that make diagrams Lorentz-invariant.
