No ducks waltz. No officers ever decline to waltz. All my poultry are ducks. Let us use the symbols D: Something is a duck, W: Something waltzes, O: Something is an officer, and P: Something is my poultry. Then the statements above can be expressed as: DW 0 W PD We can string each of these implications (or their contrapositives) to get, for example: P D W 0 The conclusion P + 50 in plain English is None of your ducks is an officer." Now consider the following statements: No one can send a letter, unless they can seal an envelope No boulders can lick things Those who cannot lick things cannot seal an envelope State each as an implication and string each implication (or its contrapositive) to conclude that "Anyone who can send a letter is not a boulder