Checking whether a point is on an object in the plane

### 26.15.1 Checking whether a point is on an object in the plane

See Section 27.11.1 for checking elements in 3D geometry.

The is_element command determines whether or not a point lies on a geometric object.

- is_element takes two arguments:
  - P, a point.
  - G, a geometric object.
- is_element(P,G) returns 1 if P is an element of G and 0 otherwise.

#### Examples

is_element(-1-i,line(0,1+i))

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is_element(i,line(0,1+i))

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