The Hawkins-Simon conditions provide necessary and sufficient criteria for the existence of a positive solution in an input-output model. Which of the following statements correctly describes the Hawkins-Simon conditions?

1. The coefficient matrix must be non-negative.
2. The determinant of the matrix formed by subtracting the input coefficients from the identity matrix must be positive.
3. The sum of each row of the input-output matrix must be less than 1.
4. The input-output model must have no redundant equations.