= Quaternary Huffman coding
= Quaternary Huffman code
{synonym}
<Huffman coding> with a four-symbol output <alphabet>, minimizing <expected codeword length> among quaternary <prefix codes>. Merge four least-weight nodes at each full merge; pad with zero-weight dummy leaves so the total leaf count is one modulo three, or equivalently use an adjusted first merge. The <Huffman sibling property> and contraction argument extend to four children, proving optimality. Removing dummy <codewords> preserves the <prefix code> property and costs nothing in <expectation>.
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