check if negating the goal is possible (avoids CTERM exception for Pure propositions)
check if negating the goal is possible (avoids CTERM exception for Pure propositions)

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle