The Source as a Tool in Automata

The source of a set of states of an automaton is introduced as the set of all predecessors of members of the set. The source is shown to be a valuable tool in proofs; it is also shown to provide new insights and directions in automata theory. Relationships are explored between the source on the one hand and, on the other, subautomata, primaries, blocks, connectivity, separation, strong connectedness, retrievability, Abelian automata, homomorphisms, and other concepts.