Gr.postscript("28505-pascal.ps",4,4)
latox=c(-0.7,3.3); latoy=c(-2,2);
par(bg="yellow")
Gr(latox,latoy,cornice=T)
x=seq(-0.7,3.3,by=0.01)
y=seq(-2,2,by=0.01)
f = function (x,y)
{u=x^2+y^2-2*x; u^2-x^2-y^2}
valori=outer(x,y,f)
Gr.livelli(x,y,valori=valori,scritte=0.5,
  livelli=setdiff(seq(-2,2,by=0.5),0))
Gr.livelli(x,y,valori=valori,spessore=2,
  colore="red",scritte=0)
dev.off()