pdf("schattierung.pdf",width=1.1,height=1.1)
par(mar=c(0,0,0,0)+0.1)
plot(0,1,type="n",xaxt="n",yaxt="n",xlab="",ylab="",xlim=c(-1,1),ylim=c(-1,1))
polygon(c(-0.9,-0.1,-0.1,-0.9,-0.9),c(-0.9,-0.9,-0.1,-0.1,-0.9),col=gray(0.4))
polygon(c(-0.9,-0.1,-0.1,-0.9,-0.9),c(0.1,0.1,0.9,0.9,0.1),col=gray(0.8))
polygon(c(0.1,0.9,0.9,0.1,0.1),c(-0.9,-0.9,-0.1,-0.1,-0.9),col=gray(0.2))
polygon(c(0.1,0.9,0.9,0.1,0.1),c(0.1,0.1,0.9,0.9,0.1),col=gray(0.6))
dev.off()