h⁢Rn,t′=hn+1(n+1)!⁢(f(n+1)⁢(ξ0)⁢ⅆⅆ⁡t⁡∏k=n0n1(t-k)+f(n+2)⁢(ξ1)⁢∏k=n0n1(t-k)),