const six_plus_nine = ['+', 6, 9];
const six_times_nine = ['*', 6, 9];
const compound1 = ['+', six_times_nine, six_plus_nine];
const compound2 = ['*', six_times_nine, compound1];
const compound3 = ['-', compound2, 3];
test("+", (t) => assert.strictEqual(eval(six_plus_nine),15));
test("compound1", (t) => assert.strictEqual(eval(compound1),69));
test("compound2", (t) => assert.strictEqual(eval(compound2),3726));
test("compound3", (t) => assert.strictEqual(eval(compound3),3723));