Backtracking
A method of solving combinatorial problems by means of an algorithm which is allowed to run forward until a dead end is reached, at which point previous steps are retraced and the algorithm is allowed to run forward again. Backtracking can greatly reduce the amount of work in an exhaustive search. Backtracking is implemented as Backtrack[s, partialQ, solutionQ] in the Wolfram Language package Combinatorica` .
Backtracking also refers to a method of drawing fractals by appropriate numbering of the corresponding tree diagram which does not require storage of intermediate results (Lauwerier 1991).
(1+e)/2

