Geodesic
Multiple Fibers of del Pezzo Fibrations
Trudy Matematicheskogo Instituta imeni V.A. Steklova, Multidimensional algebraic geometry, Tome 264 (2009), pp. 137-151.

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We prove that a terminal three-dimensional del Pezzo fibration has no fibers of multiplicity $>6$. We also obtain a rough classification of possible configurations of singular points on multiple fibers and give some examples. 
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S. Mori; Yu. G. Prokhorov. Multiple Fibers of del Pezzo Fibrations. Trudy Matematicheskogo Instituta imeni V.A. Steklova, Multidimensional algebraic geometry, Tome 264 (2009), pp. 137-151. http://geodesic.mathdoc.fr/item/TM_2009_264_a15/

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