```
A <- matrix(cbind(rep(1,6),rep(0,6),rep(0,6),rep(0,6)),nrow=6,ncol=4)
B <- matrix(cbind(rep(1,6),rep(1,6),rep(0,6),rep(0,6)),nrow=6,ncol=4)
C <- matrix(cbind(rep(1,6),rep(0,6),rep(1,6),rep(0,6)),nrow=6,ncol=4)
D <- matrix(cbind(rep(1,6),rep(0,6),rep(0,6),rep(1,6)),nrow=6,ncol=4)
X <- matrix(rbind(A,B,C,D),ncol=4)
```