Consider the following statements in respect of two-dimensional incompressible flow with velocity components u and v in x and y directions respectively:
1. The continuity equation is ∂u∂x=∂v∂y
2. The acceleration in x−direction is ax=∂u∂t+u∂u∂x+v∂u∂y
3. The condition of irrotationality is ∂u∂y=∂v∂x
4. The equation of a streamline is udy = -vdx
Which of these statement are correct?