Complex sentence: A negative claim is a colloquialism for an affirmed claim that conjects the non-existence or exclusion of something; when disputed, proof of impossibility or evidence of absence are typical methods to fulfil the burden of proof.
Split into simpler sentences: A negative claim is a colloquialism for a claim that asserts the non-existence or exclusion of something. When disputed, a proof of impossibility or an "evidence of absence" argument are typical methods to fulfill the burden of proof.