Yusuf had been staring at the token stream for hours when the pattern clicked. Byte-pair encoding merges the most frequent adjacent pair at each step, replacing both with a single new token. Step 1 merged the pair (1,2) at positions 0-1 and 4-5 into token 7 (orange). Step 2 merged (3,4) at positions 1-2 and 3-4 in the step-1 output into token 8 (azure). Step 3 would merge (7,8) at positions 0-1 and 1-2 in the step-2 output into token 9 (maroon) — the whole sequence compressing to just two symbols. He leaned back and exhaled.