Geodesic
Degenerate fibers of three-dimensional manifolds fibered into rational surfaces
Matematičeskie zametki, Tome 7 (1970) no. 2, pp. 191-202 
B. V. Martynov. Degenerate fibers of three-dimensional manifolds fibered into rational surfaces. Matematičeskie zametki, Tome 7 (1970) no. 2, pp. 191-202. http://geodesic.mathdoc.fr/item/MZM_1970_7_2_a6/
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     author = {B. V. Martynov},
     title = {Degenerate fibers of three-dimensional manifolds fibered into rational surfaces},
     journal = {Matemati\v{c}eskie zametki},
     pages = {191--202},
     year = {1970},
     volume = {7},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1970_7_2_a6/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

It is proved that the components of degenerate fibers of three-dimensional algebraic manifolds fibered into rational surfaces are rational or irrational ruled suriaces. An example is constructed of a three-dimensional algebraic manifold, fibered into rational surfaces, whose degenerate fiber contains an irrational ruled surface which cannot be eliminated by birational transformations that do not alter the common fiber.