Function walk

src/compute-engine/rubi/rubi-utils.ts:1289–1315

(e: Expression, inv: boolean)

      u.ops.filter((o) => o.has(x)).length === 1 &&
      u.ops.every((o) => !o.has(x) || monomialQ(o, ctx))
    );
  return false;
}

// Rubi SimplerQ — integer < fraction < complex < everything; ties by
// magnitude; non-numbers by leaf count.
function simplerQ(u: Expression, v: Expression): boolean {
  if (isLiteralInteger(u)) {
    if (!isLiteralInteger(v)) return true;
    const a = realNum(u)!;
    const b = realNum(v)!;
    if (a === b) return false;
    if (a === -b) return b < 0;
    return Math.abs(a) < Math.abs(b);
  }
  if (isLiteralInteger(v)) return false;
  const ur = ratParts(u);
  const vr = ratParts(v);
  if (ur) {
    if (!vr) return true;
    if (ur[1] === vr[1]) return Math.abs(ur[0]) < Math.abs(vr[0]);
    return ur[1] < vr[1];
  }
  if (vr) return false;
  return leafCount(u) < leafCount(v);
}

function leafCount(e: Expression): number {
  if (!e.ops) return 1;
  return 1 + e.ops.reduce((s, op) => s + leafCount(op), 0);