Checking if four points form a harmonic division: is_harmonic

### 13.16.15 Checking if four points form a harmonic division: is_harmonic

The is_harmonic command determines whether or not four points form a harmonic division.

- is_harmonic takes four arguments:
  P,Q,R,S, four points.
- is_harmonic(P,Q,R,S) returns 1 if P,Q,R and S form a harmonic range and returns 0 otherwise.

#### Examples

- Input:
  is_harmonic(0,2,3/2,3)
  Output:

  1

- Input:
  is_harmonic(0,1+i,1,i)
  Output:

  0