from sage.plot.plot3d.shapes2 import Line

x, y = var('x,y')


F1=plot3d(f1, (x,-2,2), (y,-2,3), color="green")
F2=plot3d(f2, (x,-2,2), (y,-2,3), color="magenta")
F3=plot3d(f3, (x,-2,2), (y,-2,3), color='blue')

L1=parametric_plot3d( (x, 3, 4), (0, 1),color="red" )
L2A=parametric_plot3d( (x, 2, 3), (0, 1),color="red")
L3A=parametric_plot3d( (0, y, 3), (2, 3),color="red")
pointA=plot3d(f1, (x,-0.1,0.1), (y,1.9,2.1), color='red')


L2B=parametric_plot3d( (0, y, 0), (0, 1),color="yellow" )
L3B=parametric_plot3d( (0, y, -1), (-1, 0),color="yellow" )
pointB=plot3d(-1, (x,-0.1,0.1), (y,-0.1,0.1), color='yellow')

def f1(x,y):
    if y>=x^2+1 : return 3
    else: return -2

def f2(x,y):
    if y<=0: return -1
    else: return -2

def f3(x,y):
    if y>=x^2+1 or y<=0: return -2
    else: return 0

All=F1+F2+F3

All.show(aspect_ratio=[1,1,1])

All=F1+F2+F3+L1+L2A+L3A+pointA
All.show(aspect_ratio=[1,1,1])

All=F1+F2+F3+L1+L2B+L3B+pointB
All.show(aspect_ratio=[1,1,1])