Constrain residual enforcement ?

I have a question that I need to solve, the problem is I couldn't understand what question asks...

It says: What constraints do the following residuals enforce?. There is an array on hand which is 2xn which is named as cur.

First example on question goes like this:

x = 1:n-1;
y = 2:n;
ans1 = cur(1,x) - cur(1,y);
ans2 = cur(2,x) - cur(2,y);

So what does it want for me to do?