Sadle=sqr(x)|sqr(y)
Sheet=10*cos(x)+50|10*sin(x)+50
Sheet Folded=20*cos(3*x)+50|10*sin(y)+50
Sheet Double Folded=20*cos(3*x)+50|10*sin(5*y)+50
Enclosing=x^2-2*x+1.27|y^2-3*y+3