Rannacher–Turek

\(\mathcal{P}_k=\operatorname{span}\left\{\prod_{i=1}^dx_i^{p_i}\middle|\sum_{i=1}^dp_i\leqslant k\right\}\)

\(\mathcal{Z}^{(24)}_k=\operatorname{span}\left\{(x_1+x_2)(x_1-x_2)\right\}\)

\(\mathcal{Z}^{(25)}_k=\operatorname{span}\left\{(x_1+x_2)(x_1-x_2),(x_2+x_3)(x_2-x_3))\right\}\)

Before trying this example, you must install Symfem:

pip3 install symfem

This element can then be created with the following lines of Python:

import symfem

# Create Rannacher-Turek order 1 on a quadrilateral
element = symfem.create_element("quadrilateral", "Rannacher-Turek", 1)