Dehn surgeries that yield fibred 3--manifolds

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We study Dehn surgeries on null-homotopic knots that yield fibred 3--manifolds when an additional (but natural) homological restriction is imposed. The major tool used is Gabai's theory of sutured manifold decomposition. Such surgeries are negative examples to a question of Michel Boileau. Another result we will prove is about surgeries which reduce the Thurston norm of a fibred manifold.