A parallelogram height inequality for Drinfeld modules

We prove inequalities relating the Taguchi heights, respectively the graded heights, of four Drinfeld modules arranged in a ``parallelogram of isogenies’'. This inequality is the analogue for Drinfeld modules of the parallelogram inequality of Rémond (2022) for abelian varieties over number fields and of Griffon–Le Fourn–Pazuki (2025) for abelian varieties over function fields.