Function equalOrder

src/compute-engine/boxed-expression/order.ts:125–154

(a: Expression, b: Expression)

    if (aLex < bLex) return -1;
    if (aLex > bLex) return +1;
  }
  return order(a, b);
}

/**
 * Sort terms of a sum with `addOrder` semantics, computing each term's
 * degree/lexicographic keys once instead of on every comparison (`addOrder`
 * re-walks both expressions per comparison — O(n log n) walks per sort).
 * The comparator chain below returns exactly the values `addOrder` would,
 * and `Array.sort` is stable, so the result order is identical.
 */
export function sortAddTerms(
  xs: ReadonlyArray<Expression>
): ReadonlyArray<Expression> {
  if (xs.length <= 1) return [...xs];
  const keyed = xs.map((x) => ({
    x,
    total: totalDegree(x),
    max: maxDegree(x),
    lex: revlex(x),
  }));
  keyed.sort((a, b) => {
    if (a.total !== b.total) return b.total - a.total;
    if (a.max !== b.max) return b.max - a.max;
    if (a.lex || b.lex) {
      if (!a.lex) return +1;
      if (!b.lex) return -1;
      if (a.lex < b.lex) return -1;
      if (a.lex > b.lex) return +1;
    }
    return order(a.x, b.x);
  });
  return keyed.map((k) => k.x);