A Fibonacci word is a specific sequence of binary digits (or symbols from any two-letter alphabet). The Fibonacci word is formed by repeated concatenation in the same way that the Fibonacci numbers are formed by repeated addition. It is a paradigmatic example of a Sturmian word and specifically, a morphic word. The name "Fibonacci word" has also been used to refer to the members of a formal language L consisting of strings of zeros and ones with no two repeated ones. Any prefix of the specific Fibonacci word belongs to L, but so do many other strings. L has a Fibonacci number of members of each possible length. Definition Let be "0" and be "01". Now (the concatenation of the previous sequence and the one before that). The infinite Fibonacci word is the limit , that is, the (unique) infinite sequence that contains each , for finite , as a prefix. Enumerating items from the above definition produces: 0 01 010 01001 01001010 0100101001001 ... The first few elements of the infinite Fibonacci word are: 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, ... Closed-form expression for individual digits The nth digit of the word is where is the golden ratio and is the floor function . As a consequence, the infinite Fibonacci word can be characterized by a cutting sequence of a line of slope or . See the figure above. Substitution rules Another way of going from Sn to Sn&hairsp;+1 is to replace each symbol 0 in Sn with the pair of consecutive symbols 0, 1 in Sn&hairsp;+1, and to replace each symbol 1 in Sn with the single symbol 0 in Sn&hairsp;+1. Alternatively, one can imagine directly generating the entire infinite Fibonacci word by the following process: start with a cursor pointing to the single digit 0. Then, at each step, if the cursor is pointing