leontiff input-output matrix

[Neha Gupta]

In an open economy Input-Output model, A is the input-coefficients matrix, the viability
condition to be satisfied is:
(1) |I – A| ≠ 0
(2) |I – A| > 0
(3) |I – A| < 0
(4) All principal minors of the matrix (I – A) must be positive.

(correct ans= 4), please anyone tell how?