Function check2F1

test/compute-engine/special-functions.test.ts:1267–1276

(
    args: (number | unknown[])[],
    re: number,
    im: number,
    tol = 1e-12
  )

});

// Exponential and logarithmic integrals (ROADMAP B2: ∫eˣ/x → Ei,
// ∫1/ln x → li). Machine-precision only (no bignum kernel; ROADMAP B1).
describe('EXPONENTIAL & LOGARITHMIC INTEGRALS (Ei, li)', () => {
  test('Ei(1) ≈ 1.8951178163559368', () =>
    expectApprox(ce.expr(['ExpIntegralEi', 1]), 1.8951178163559368, 1e-12));

  test('Ei(2) ≈ 4.954234356001890 (asymptotic-free regime)', () =>
    expectApprox(ce.expr(['ExpIntegralEi', 2]), 4.95423435600189, 1e-12));

  test('Ei(10) ≈ 2492.2289762418777', () =>
    expectApprox(ce.expr(['ExpIntegralEi', 10]), 2492.2289762418777, 1e-9));

  test('Ei(40) ≈ 6.0397182636112e15 (asymptotic-series regime)', () =>