problems

By the way:

(%i2) :lisp(defun manifestly-pure-imaginary-p (e) (eq '$imaginary ($csign e)));
MANIFESTLY-PURE-IMAGINARY-P

(%i2) map(lambda([s], print(facts()), conjugate(s)), [1/sqrt(x),1/sqrt(x)]);
[]
[notequal(x,0)]
(%o2) [conjugate(1/sqrt(x)),1/sqrt(x)]

A conservative approach might be

(defun conjugate-mexpt (e)
  (let ((x (first e)) (p (second e)))
    (cond ((or (off-negative-real-axisp x) ($featurep p '$integer))
	   (power (take '($conjugate) x) (take '($conjugate) p)))
	  ((and (on-negative-real-axisp x) (manifestly-real-p p))
	   (mul -1 (power x p)))


Then

 (%i3) assume(a > b);
 (%o3) [a>b]

 (%i5) conjugate(sqrt(b-a));
 (%o5) -sqrt(b-a)

--Barton