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S Aug 12, 2013 at 9:54 history suggested Michael Albanese CC BY-SA 3.0
Replaced \\# by \#.
Aug 12, 2013 at 9:52 review Suggested edits
S Aug 12, 2013 at 9:54
Jun 2, 2013 at 6:05 comment added Jun Li I'm sorry for the ambiguous.The map $b$ is in general not surjective.$X$ and $Y$ are both smooth and connected.Thank you for the comments.
May 31, 2013 at 17:02 history edited user9072 CC BY-SA 3.0
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May 31, 2013 at 15:09 comment added user30180 If $X$ is connected and $b$ is surjective then $X$ and $Y$ have the same dimension at all points, so $b$ is necessarily flat (in the sense of maps of local rings), so the coherent sheaf $b_{\ast}(O_X)$ is a vector bundle on $Y$. The rank of this vector bundle must be constant since $Y$ is connected, and it provides a uniform upper bound on the size of fibers. Are you interested in cases with either $X$ disconnected or $b$ not surjective?
May 31, 2013 at 14:48 comment added user30180 You must be assuming $Y$ is connected. Are you assuming $X$ is connected or $b$ is surjective? It is false without at least one of those, so please state all of your hypotheses.
May 31, 2013 at 13:16 history asked Jun Li CC BY-SA 3.0