+relational::safe_bool relational::make_safe_bool(bool cond) const
+{
+ return cond? &safe_bool_helper::nonnull : nullptr;
+}
+
+/** Cast the relational into a Boolean, mainly for evaluation within an
+ * if-statement. Note that (a<b) == false does not imply (a>=b) == true in
+ * the general symbolic case. A false result means the comparison is either
+ * false or undecidable (except of course for !=, where true means either
+ * unequal or undecidable). */
+relational::operator relational::safe_bool() const
+{
+ const ex df = lh-rh; // like ::canonical() method
+ // We treat numeric and symbolic expression differently
+ if (is_exactly_a<numeric>(df)) {
+ switch (o) {
+ case equal:
+ return make_safe_bool(ex_to<numeric>(df).is_zero());
+ case not_equal:
+ return make_safe_bool(!ex_to<numeric>(df).is_zero());
+ case less:
+ return make_safe_bool(ex_to<numeric>(df)<(*_num0_p));
+ case less_or_equal:
+ return make_safe_bool(ex_to<numeric>(df)<=(*_num0_p));
+ case greater:
+ return make_safe_bool(ex_to<numeric>(df)>(*_num0_p));
+ case greater_or_equal:
+ return make_safe_bool(ex_to<numeric>(df)>=(*_num0_p));
+ default:
+ throw(std::logic_error("invalid relational operator"));
+ }
+ } else {
+ // The conversion for symbolic expressions is based on the info flags
+ switch (o) {
+ case equal:
+ return make_safe_bool(df.is_zero());
+ case not_equal:
+ return make_safe_bool(! df.is_zero());
+ case less:
+ return make_safe_bool(df.info(info_flags::negative));
+ case less_or_equal:
+ return make_safe_bool((-df).info(info_flags::nonnegative));
+ case greater:
+ return make_safe_bool(df.info(info_flags::positive));
+ case greater_or_equal:
+ return make_safe_bool(df.info(info_flags::nonnegative));
+ default:
+ throw(std::logic_error("invalid relational operator"));
+ }
+ }
+}
+
+/** Returns an equivalent relational with zero right-hand side.
+ */
+ex relational::canonical() const
+{
+ return relational(lh-rh, _ex0, o);
+}