determine the corresponding scattering amplitude even when its asymptotic behavior is not the physical one. The discussion presented here is limited to systems with A = 2 , 3. This is because our expertise to calculate few-nucleon wave functions is limited to these systems. However applications to heavier systems are possible and, in particular, it would be interesting to analyze the use of the GFMC method in the computation of the integral relations in systems with A > 4. The paper is organized as follows: in Section II the integral relations are derived from the KVP. Applications to the two- and three-body systems are given in Section III and IV, respectively, whereas applications of the integral relations in connection with the HA are given in Section V. The conclusions are given in the last section. In order to derive the integral relations we first consider a two-body system interacting through a short-range potential V ( r ) at the center of mass energy E in a relative angular momentum state l = 0. The solution of the Schr¨ odinger equation in configuration space ( m is twice the reduced mass), can be obtained after specifying the corresponding boundary conditions. For E > 0, with k 2 = E/ ( ℏ $^{2}$/m ) and assuming a short-range potential V , Ψ( r ) = φ ( r ) $_{/}$√$_{4}$$_{π}$ and from which one gets Ψ → AF + BG , where Use of the Wronskian theorem immediately leads to the following general expressions for the coefficients A and B : 4 B = m ℏ 2 [ < F | H − E | Ψ > − < Ψ | H − E | F > ] A = m ℏ 2 [ < Ψ | H − E | G > − < G | H − E | Ψ > ] , (4) F = √ k 4 π sin( kr ) kr G = k 4 π cos( kr ) kr . (3) φ ( r → ∞ ) −→ √$_{k}$ [ A sin( kr ) kr + B cos( kr ) kr ] . (2) ( H − E )Ψ( r ) = ( − ℏ 2 m ∇ 2 + V − E )Ψ( r ) = 0 , (1) II. INTEGRAL RELATIONS FROM THE KOHN VARIATIONAL PRINCIPLE