Abstract: Deeper structures behind BPS counting on toric Calabi-Yau 3-folds have recently been realized mathematically in terms of the quantum loop group associated to a certain quiver drawn on a torus, which is endowed with an action on the BPS vector space via crystal melting. In this talk, we identify the annihilator of the aforementioned action, thus leading to the definition of a reduced quantum loop group associated to a toric Calabi-Yau 3-fold satisfying a certain consistency condition we call “shrubbiness”.