Checking if four points are concyclic in the plane: is_concyclic

### 13.16.3 Checking if four points are concyclic in the plane: is_concyclic

See Section 14.13.7 for checking for concyclicity in three-dimensional geometry.

The is_concyclic command determines whether or not points are cyclic.

- is_concyclic takes one argument:
  L, a list or sequence of points.
- is_concyclic(L) returns 1 if the points in L all lie on the same circle, and returns 0 otherwise.

Examples.

- Input:
  is_concyclic(1+i, -1+i, -1-i, 1-i)
  Output:

  1

- Input:
  is_concyclic(i, -1+i, -1-i, 1-i)
  Output:

  0