doctests and minor edits

Author: DaveWitteMorris

build/pkgs/pynac/package-version.txt

@@ -1 +1 @@
-0.7.26.sage-2020-04-03.p0
+0.7.26.sage-2020-04-03.p2

build/pkgs/pynac/patches/power_inf_loop.patch

@@ -1,19 +1,21 @@
 diff --git a/ginac/power.cpp b/ginac/power.cpp
 --- a/ginac/power.cpp
 +++ b/ginac/power.cpp
-@@ -920,10 +920,11 @@
+@@ -920,10 +920,14 @@
  			const ex& e = m.recombine_pair_to_ex(elem);
  			if (e.is_positive())
  				prodseq.push_back(pow(e, exponent).expand(options));
 -			else if (e.info(info_flags::negative)) {
 -				prodseq.push_back(pow(-e, exponent).expand(options));
 -				possign = !possign;
 -			} else
++// 			we delete the following 'else if' clause because it can lead to
++// 			an infinite loop (see sagemath :trac:`30688`)
++// 			TODO: find a bug-free treatment of negative factors
 +// 			else if (e.info(info_flags::negative)) {
 +// 				prodseq.push_back(pow(-e, exponent).expand(options));
 +// 				possign = !possign;
 +// 			}
 +			else
  				powseq.push_back(elem);
  		}
- 

src/sage/symbolic/expression.pyx

@@ -4807,6 +4807,14 @@ cdef class Expression(CommutativeRingElement):
             1/(x^2 + 2*x + 1)
             sage: (((x-1)/(x+1))^2).expand()
             x^2/(x^2 + 2*x + 1) - 2*x/(x^2 + 2*x + 1) + 1/(x^2 + 2*x + 1)
+
+        Check that :trac:`30688` is fixed::
+
+            sage: assume(x < 0)
+            sage: sqrt(-x).expand()
+            sqrt(-x)
+            sage: ((-x)^(3/4)).expand()
+            (-x)^(3/4)
         """
         if side is not None:
             if not is_a_relational(self._gobj):