### 11.9.4 Parallelograms in the plane: parallelogram

See section 12.8.4 for parallelograms in space.

The parallelogram command takes three mandatory arguments and one optional argument. The mandatory arguments are three points A, B and C.

parallelogram returns and draws the parallelogram ABCD for the appropriate D.
Input:

parallelogram(0, 1, 2 + i)

Output:

The fourth optional argument will need to be a variable name which will be assigned to vertex D.
Input:

parallelogram(0, 1, 2 + i, D)

Output:

Input:

affix(D)

Output:

1 + i