Horseback riding is an either/or situation.
How you approach the potty training issue really boils down to your choice, and it doesn't have to be an either/or approach.
The limitation to this is that one can not claim both state and local tax deduction and the deduction for sales tax, it is an either/or situation.
Where you learn to play Brazilian guitar chords isn't an either/or proposition.
Some new car warranties are also the either/or variety-for example, "five years or 50,000 miles".
Although PKU conforms to these basic genetic patterns of inheritance, the actual expression, or phenotype, of the disease is not strictly an either/or situation.