(1) -> x := interval(-2.0,-1.0)$Interval Float

   (1)  [- 2.0, - 1.0]
                               Type: Interval(Float)
(2) -> x^(2/1)

   (2)  [0.0, 4.0000000000_000000001]
                               Type: Interval(Float)
(3) -> x^2

   (3)  [0.9999999999_9999999999, 4.0000000000_000000001]
                                Type: Interval(Float)


Notice that for the fractional power (2/1), the answer is wrong.

- Qian

diff --git a/src/algebra/interval.spad b/src/algebra/interval.spad
index 180b1c7b..8bd84ec1 100644
--- a/src/algebra/interval.spad
+++ b/src/algebra/interval.spad
@@ -429,7 +429,7 @@
                error "fractional power only defined for x > 0"
            even?(numer(n)) =>
                hi < 0 =>
-                   interval(0, lo^n)
+                   interval(hi^n, lo^n)
                interval(0, max(lo^n, hi^n))
            interval(lo^n, hi^n)
       interval(lo^n, hi^n)

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