timelets

...from which was born Ericthonius, a man well made and handsome in the upper parts of the body, but with thighs and legs like an eel, thin and deformed: and that he, from consciousness of this deformity, first invented chariots, whereby he might shew off the fine part of his body and hide the mean.

Francis Bacon, Of the Wisdom of the Ancients, XX.

We can think about a normal human as an implementation (object & an inclusion map) for personal transportation: legs both enable and limit our ability to move. Replacing legs with the chariot extends the range, i.e. represents a different object and an inclusion map. Note that the human is still in control. As the result we have a parameterized family of maps:

Control x Conveyance {legs, chariot} -> Transfer.