The Weak Graded Lie 2-Algebra of Multiplicative Forms on a Quasi-Poisson Groupoid

We present a construction of weak graded Lie 2-algebras associated with quasi-Poisson groupoids. We also establish a morphism between this weak graded Lie 2-algebra of multiplicative forms and the strict graded Lie 2-algebra of multiplicative multivector fields, allowing us to compare and relate different aspects of Lie 2-algebra theory within the context of quasi-Poisson geometry. As an infinitesimal analogy, we explicitly determine the associated weak graded Lie 2-algebra structure of IM forms for any quasi-Lie bialgebroid.