+/** Get numerator and denominator of an expression. If the expresison is not
+ * of the normal form "numerator/denominator", it is first converted to this
+ * form and then a list [numerator, denominator] is returned.
+ *
+ * @see ex::normal
+ * @return a list [numerator, denominator] */
+ex ex::numer_denom(void) const
+{
+ lst sym_lst, repl_lst;
+
+ ex e = bp->normal(sym_lst, repl_lst, 0);
+ GINAC_ASSERT(is_ex_of_type(e, lst));
+
+ // Re-insert replaced symbols
+ if (sym_lst.nops() > 0)
+ return e.subs(sym_lst, repl_lst);
+ else
+ return e;
+}
+