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Original question demonstrated to be the wrong thing to ask. Modified it accordingly.
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Emre
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Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions, can we assume that $f \colon X \to Y$ is finite?

Edit: This too is not enough as Piotr demonstrates in the comments. The key observation is that finiteness is not local on the source and even an open immersion is a counterexample to the question above.

Let me then modify the question like so:

Modified question: What global criteria, such as properness, on the morphism $f:X \to Y$ need to be assumed to make finiteness (formal) local on the source?

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions, can we assume that $f \colon X \to Y$ is finite?

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions, can we assume that $f \colon X \to Y$ is finite?

Edit: This too is not enough as Piotr demonstrates in the comments. The key observation is that finiteness is not local on the source and even an open immersion is a counterexample to the question above.

Let me then modify the question like so:

Modified question: What global criteria, such as properness, on the morphism $f:X \to Y$ need to be assumed to make finiteness (formal) local on the source?

added 8 characters in body
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Francesco Polizzi
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Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions, can we assume that $X \to Y$$f \colon X \to Y$ is finite?

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions can we assume that $X \to Y$ is finite?

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions, can we assume that $f \colon X \to Y$ is finite?

added 26 characters in body; edited tags; edited title
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Francesco Polizzi
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Is there a formal local criterion of finiteness?

Vaguely

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Specifically

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions can we assume that $X \to Y$ is finite?

Is there a formal local criterion of finiteness

Vaguely

Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Specifically

Suppose $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Under these conditions can we assume $X \to Y$ is finite?

Is there a formal local criterion of finiteness?

Vague question: Is there a criterion to deduce that a morphism between algebraic stacks is finite based on the local deformation functors?

For sure this is not enough, so let me be more specific.

Suppose that $f: X \to Y$ is a morphism of algebraic stacks. Let us assume in addition that the diagonal $\Delta_f : X \to X \times_Y X$ is finite and unramified.

Now assume that for each point $x \in |X|$ of finite type over $y \in |Y|$ the morphism between the (pro-representing rings of the) deformation functors is finite.

Specific question: Under these conditions can we assume that $X \to Y$ is finite?

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Emre
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