Lemma 101.5.4. Let f : \mathcal{X} \to \mathcal{Y} be a morphism of algebraic stacks. Let Z be an algebraic space and let x_ i : Z \to \mathcal{X}, i = 1, 2 be morphisms. Then
\mathit{Isom}_{\mathcal{X}/\mathcal{Y}}(x_2, x_2) is a group algebraic space over Z,
there is an exact sequence of groups
0 \to \mathit{Isom}_{\mathcal{X}/\mathcal{Y}}(x_2, x_2) \to \mathit{Isom}_\mathcal {X}(x_2, x_2) \to \mathit{Isom}_\mathcal {Y}(f \circ x_2, f \circ x_2)there is a map of algebraic spaces \mathit{Isom}_\mathcal {X}(x_1, x_2) \to \mathit{Isom}_\mathcal {Y}(f \circ x_1, f \circ x_2) such that for any 2-morphism \alpha : f \circ x_1 \to f \circ x_2 we obtain a cartesian diagram
\xymatrix{ \mathit{Isom}_{\mathcal{X}/\mathcal{Y}}^\alpha (x_1, x_2) \ar[d] \ar[r] & Z \ar[d]^\alpha \\ \mathit{Isom}_\mathcal {X}(x_1, x_2) \ar[r] & \mathit{Isom}_\mathcal {Y}(f \circ x_1, f \circ x_2) }for any 2-morphism \alpha : f \circ x_1 \to f \circ x_2 the algebraic space \mathit{Isom}_{\mathcal{X}/\mathcal{Y}}^\alpha (x_1, x_2) is a pseudo torsor for \mathit{Isom}_{\mathcal{X}/\mathcal{Y}}(x_2, x_2) over Z.
Comments (0)
There are also: