The is_parallelogram command takes as argument a geometric object or four points.
is_parallelogram returns 1, 2, 3
or 4 if the object is a parallelogram. It returns 4
if the object is a square, 3 if the object is a rectangle but
not a square, 2 if the object is a rhombus but not a
rectangle, and returns 1 otherwise. The command returns
0 if the object is not a parallelogram.
Input:
Output:
Input:
Output:
Input:
then:
Output:
Input:
then:
Output:
Note that P[0] is a parallelogram since P is a list made
of a parallelogram and vertex D. Entering
affix(D) returns -2+i.