# Checking if an object in the plane is a square: is_square

### 13.16.8 Checking if an object in the plane is a square: is_square

See Section 14.13.12 for checking for squares in three-dimensional geometry.

The is_square command determines whether or not a geometric object is a square.

- is_square takes one argument:
  G, a geometric object or a sequence of four points assumed to be the vertices of a quadrilateral.
- is_square(G) returns 1 if the object is a square and returns 0 otherwise.

#### Examples.

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

  1

- Input:

  K:= square(1+i, -1+i)
  is_square(K)

  Output:

  1

- Input:

  K:= square(1+i, -1+i, C, D)
  is_square(K[0])

  Output:

  1

  Note that K[0] is a square since K is a list made of a square and vertices C and D.
  Input:
  affix(C,D)
  Output:

  −1−i,1−i

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

  0