We shall also refer to a point as backward nonsingular, with the obvious analogous meaning.
The notion of backward complete is defined analogously by exchanging the roles of f and f-1.
Extend this sequence of numbers backwards, defining N-1, N-2 and N-3 by......
Then G is simply g with its periodic string read backwards.
[In most adverbial uses, backward and backwards are interchangeable; as an adjective, the more standard form is backward: a backward shift.]