  We consider the 3D incompressible Euler equations under the following
situation: small-scale vortex blob being stretched by a prescribed large-scale
stationary flow. More precisely, we clarify what kind of large-scale stationary
flows really stretch small-scale vortex blobs in alignment with the straining
direction. The key idea is constructing a Lagrangian coordinate so that the Lie
bracket is identically zero (c.f. the Frobenius theorem), and investigate the
locality of the pressure term by using it.
