moved nonzero_mult_divide_cancel_right to Ring_and_Field as nonzero_mult_divide_cancel_right'; tuned proofs
moved nonzero_mult_divide_cancel_right to Ring_and_Field as nonzero_mult_divide_cancel_right'; tuned proofs

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