If yeast rises then caustic potash is present and if mold grows then limewater is present. Either caustic potash is not present or limewater is not present. Either yeast does not rise or mold does not grow. Limewater is present. Yeast rises and limewater is present.
Some antigens are serums.
All serums are donors. All donors are serums. Some donors are not antigens. All antigens are not serums. Some donors are antigens.