another property
if two adjacent rows of a matrix A are equal,then
let us prove this fact by induction on N
suppose that rows J and J+1 are equal
then the matrices A defined by (3.3) also have two rows equal,except when
when A has two equal rows ,its determinant is zero by induction
thus only two terms of (3.4) are different from zero
moreover,since the rows R and S are equal,it follows that sth
since the signs alternate,the two terms on the right side cancel,and the determinant is zero