Function mmaTermKey

src/compute-engine/rubi/rubi-utils.ts:1147–1153

sorted symbol leaves of a term, reversed (MMA compares monomials from * their trailing factor)

(e: Expression)

// Rubi PosAux (sign heuristic): numbers by value; symbols positive;
// products multiply signs; sums take the first term; even powers positive.
function posAux(u: Expression): boolean {
  const r = realNum(u);
  if (r !== null) return r > 0;
  const n = u.N();
  if (isNumber(n) && typeof n.re === 'number' && typeof n.im === 'number') {
    return n.re !== 0 ? n.re > 0 : n.im > 0;
  }
  if (u.symbol) return true;
  if (u.operator === 'Power' && u.ops) {
    const e = u.ops[1];