Check if an object in space is on another object: is_element

### 13.13.1 Check if an object in space is on another object: is_element

See section 12.16.1 for checking elements in two-dimensional geometry.

The is_element command takes as arguments two geometric objects.

is_element returns 1 is the first object is contained in the second, it returns 0 otherwise.

Input:

P := plane([0,0,0],[1,2,-3],[1,1,-2])

then:

is_element(point(2,3,-5),P)

Output:

1

Input:

L := line([2,3,-2],[-1,-1,-1]);
P := plane([-1,-1,-1],[1,2,-3],[1,1,-2])

then:

is_element(L,P)

Output:

0