arreglo <- array(0, c(7,7));
i <- array(c(1:4,4:1), dim=c(4,2));
arreglo[i] <- 1;
i1 <- array(c(4:7,1:4), dim=c(4,2));
arreglo[i1] <- 1;
i2 <- array(c(1:4,4:7), dim=c(4,2));
arreglo[i2] <- 1;
i3 <- array(c(4:7,7:4), dim=c(4,2));
arreglo[i3] <- 1;
arreglo