user since
Wed Jun 14 2000 at 23:39:05 (17.5 years ago )
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Sun Jul 7 2002 at 02:04:31 (15.4 years ago )
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philosophy, mathematics, linguistics
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University of Kentucky
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"If you give the principal a cracker soaked in liquid nitrogen, fog will come out of his nose!" --Joe Manfre
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discontinuous identity map
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semicontinuous function

One way to define usc (lsc):

A function f is upper semicontinuous at a point x_0 if either f(x_0)=\infty or for each M > f(x_0), there is a positive \delta such that if |x-x_0| < \delta, then M > f(x). f is lower semicontinous at x_0 if -f is upper semicontinuous at x_0.