Title: Complementary legs and rational balls,
Abstract: In this note we study the Seifert rational homology spheres with two
complementary legs, i.e. with a pair of invariants whose fractions add up to
one. We give a complete classification of the Seifert manifolds with 3
exceptional fibers and two complementary legs which bound rational homology
balls. The result translates in a statement on the sliceness of some Montesinos
knots.