Function polyCoeffsX

src/compute-engine/rubi/rubi-utils.ts:351–359

(u: Expression, x: string)

      if (m0 === null || m1 === null) return null;
      return [
        ...m0,
        ...m1.map(([c, d]) => [c.neg(), d] as [Expression, number]),
      ];
    }
    case 'Divide': {
      if (ops[1].has(x)) return null;
      const m = monomialsX(ops[0], x);
      return m === null ? null : m.map(([c, d]) => [c.div(ops[1]), d]);
    }
    case 'Power': {
      const e = realNum(ops[1]);
      if (e === null || !Number.isInteger(e) || e < 0) return null;