Linear program with $\pm 1$ constraints I am trying to formulate a constraint as follows ($X, Y, Z$ are either $-1$ or $1$): 
If $Z$ and $Y$ both equal $-1$, then $X$ must be $1$. But, if either $Z$ or $Y$ are not $-1$, then $X$ can be $-1$ or $1$.
I came up with $Z\cdot Y \le X$, but that limits $X$ to $1$ if both $Z$ and $Y$ are $1$ ($X$ can be $0$ if both are $1$).
Any advice on a more accurate constraint? 
Thank you.

Note: If you're trying to keep a linear program, do not add constraints of the form ZY
My solution: $-3(Y+Z)\leq 5+X$
I am not sure if a better solution exists, however!
