Sequences of letters
Source: 44th International Tournament of Towns, Senior A-Level P1, Spring 2023
April 4, 2023
combinatorics
Problem Statement
There are two letter sequences and , both with length letters. In one move you can insert in any place of sequence ( possibly to start or to end) any number of same letters or remove any number of consecutive same letters.
Prove that it is possible to make second sequence from first sequence using not more than moves.