(Adapted from Barwise+Etchemendy:1993 .) Given the following, can you prove that the unicorn is mythical? How about magical? Horned?
Note: If the unicorn is mythical, then it is immortal, but if it is not mythical, then it is a mortal mammal. If the unicorn is either immortal or a mammal, then it is horned. The unicorn is magical if it is horned.