If the drug interdiction program is strengthened only if heroin becomes more readily available, then either the number of addicts is decreasing or the war on drugs is failing. If the drug interdiction program is strengthened, then smugglers will shift to more-easily concealable drugs. If smugglers shift to more-easily concealable drugs, then heroin will become more readily available. Furthermore, the number of addicts is not decreasing. Therefore, the war on drugs is failing. (D, H, N, W, S)

Translate the following arguments into symbolic form and use the first four rules of inference to derive the conclusion of each. The letters to be used for the simple statements are given in parentheses after each exercise. Use these letters in the order in which they are listed.