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Mathematicians are great. They have recently shown us how to maximise our lottery winnings; at what stage of emptiness our beer cans are most unstable; and to walk in the rain because running leaves us no drier.

Now a Manchester mathematician has undermined the idea behind president Ragan's Star Wars anti-missile system. John Gilder points out that any projectile launched from earth will follow a curving path - a parabola. And each parabola belongs to a family of parabolas. And this family is itself enveloped in one big parabola - the parabolic envelope. So, says Dr Gilder, of UMIST, if you launch your missile along this parabolic envelope you are guaranteed to hit any enemy missile moving along any parabola in the family. Who needs Star Wars?