Fix bug in differentiation of a power.

diff --git a/ginac/power.cpp b/ginac/power.cpp
index 95a01acec2b5d31c4312ced86020990d99dc4fd7..0ebc8dc29a20db47796cde8ab228eb293c76d3da 100644 (file)
--- a/ginac/power.cpp
+++ b/ginac/power.cpp
@@ -620,7 +620,7 @@ ex power::conjugate() const
  *  @see ex::diff */
 ex power::derivative(const symbol & s) const
 {
-       if (exponent.info(info_flags::real)) {
+       if (is_a<numeric>(exponent)) {
                // D(b^r) = r * b^(r-1) * D(b) (faster than the formula below)
                epvector newseq;
                newseq.reserve(2);