Logic: Problem 3

Hints for (a)

You can think of unique existence as making two claims.

  1. There is (at least) one value with the stated property.
  2. There isn't a second value with the stated property. Or, if you like, there can't be two distinct values with that property.

Remember that setting up two differently-named variables x and y does not imply (in mathematics) that x and y have different values. If you need them to be different, you need to explicitly state that \(x \not = y\).