Birational invariant
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In mathematics, a birational invariant in algebraic geometry is a quantity or object that is well-defined on a birational equivalence class of algebraic varieties. In other words, it depends only on the function field of the variety.
For example in the case of an algebraic surface, the Hodge numbers h0,1 and h0,2 of a non-singular projective complex surface are birational invariants. The Hodge number h1,1 is not, since the process of blowing up a point to a curve on the surface can augment it.
