levelSet1= {x | f(x) <= 1} with f=
[x,y]->[x^4 + y^4]
levelSet1 contains  [-0.5, -0.5] ?  True
levelSet1 contains  [0.5, 0.0] ?  True
levelSet1 contains  [1.5, 0.0] ?  False
levelSet2= {x | f(x) <= 1} with f=
[x,y]->[(x-1)^2 + y^2]
levelSet2 contains  [-0.5, -0.5] ?  False
levelSet2 contains  [0.5, 0.0] ?  True
levelSet2 contains  [1.5, 0.0] ?  True
intersection of  {x | f(x) <= 1} with f=
[x,y]->[x^4 + y^4]  and  {x | f(x) <= 1} with f=
[x,y]->[(x-1)^2 + y^2]  equals  {x | f(x) <= 0} with f=
([x0,x1]->[max(x0 - 1, x1 - 1)])o([[x,y]->[x^4 + y^4],[x,y]->[(x-1)^2 + y^2]])
intersection contains  [-0.5, -0.5] ?  False
intersection contains  [0.5, 0.0] ?  True
intersection contains  [1.5, 0.0] ?  False
join of  {x | f(x) <= 1} with f=
[x,y]->[x^4 + y^4]  and  {x | f(x) <= 1} with f=
[x,y]->[(x-1)^2 + y^2]  equals  {x | f(x) <= 0} with f=
([x0,x1]->[min(x0 - 1, x1 - 1)])o([[x,y]->[x^4 + y^4],[x,y]->[(x-1)^2 + y^2]])
join contains  [-0.5, -0.5] ?  True
join contains  [0.5, 0.0] ?  True
join contains  [1.5, 0.0] ?  True
