  Given a submanifold Z inside X, let Y be the blow-up of X along Z. When the
normal bundle of Z in X is convex with a minor assumption, we prove that
genus-zero GW-invariants of Y with cohomology insertions from X, are identical
to GW-invariants of X. Under the same hypothesis, a vanishing theorem is also
proved. An example to which these two theorems apply is when the normal bundle
is generated by global sections. These two main theorems do not hold for
arbitrary blow-ups, and counter-examples are included.
