Complex sentence: The sum of the two however results in the propagation of light energy in the usual causal way, in which the absorption is later than the emission, but the anti-causal (advanced) solution direction is not discarder "a priori".
Split into simpler sentences: The sum of the two however results in the usual "causal waves", whith the absorption later than the emission. The anti-causal (advanced) solution however is not discarder "a priori".