Rationalized the theorem if_image_distrib. Added parens to not_empty.
Rationalized the theorem if_image_distrib.
Added parens to not_empty.

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