Letter Keys - ILL 1990 ISR1
Source:
September 18, 2010
combinatorics solvedcombinatorics
Problem Statement
Given three letters , we can construct letter sequences arbitrarily, such as , etc. For any given sequence, we can perform following operations:: If the right-most letter is , then we can add after it, for example, : If The sequence contains , we can replace them by , for example, : We can replace ( is any sub-sequence) by , for example, : In a sequence containing one or more , we can replace the first by , for example,
: We can replace any of by , for example, or or Using above operations, can we get from