Consider the string of length 6 composed of three characters a,b,c. For each string, if two as are next to each other, or two bs are next to each other, then replace aa by b, and replace bb by a. Also, if a and b are next to each other, or two cs are next to each other, remove all two of them (i.e. delete ab,ba,cc). Determine the number of strings that can be reduced to c, the string of length 1, by the reducing processes mentioned above. combinatoricsCombinatorics of wordscountingpermutations