Fix axiom that states 0.0 ^ (-1) = 0.0 in real.PowerReal theory.

Remove the incorrect Coq realization of PowerReal.pow by Rpower, since the
latter is only meaningfully defined for positive first arguments, e.g.
Rpower (-1) 3 = 1!

drivers/coq-common.gen

@@ -274,15 +274,6 @@ theory real.PowerInt
   (* remove prop Power_sum *) (* not the same as powerRZ_add *)
   (* remove prop Power_mult *)
 
-
-end
-
-theory real.PowerReal
-
-  prelude "Require Import Rpower."
-
-  syntax function pow "(Rpower %1 %2)"
-
 end
 
 theory real.Trigonometry

theories/real.why

@@ -253,7 +253,7 @@ theory PowerReal
   function pow real real : real
 
   axiom Pow_zero_y:
-    forall y:real. y <> 0.0 -> pow 0.0 y = 0.0
+    forall y:real. y > 0.0 -> pow 0.0 y = 0.0
 
   axiom Pow_x_zero:
     forall x:real. x <> 0.0 -> pow x 0.0 = 1.0