After https://github.com/boostorg/logic/commit/23cd89d4c80f build fails:

src/AIEcho.cpp:4390:9: error: no viable conversion from returned value of type 'boost::logic::tribool' to function return type 'bool'
        return is_end!=rhs.is_end || team!=rhs.team || building_type!=rhs.building_type || level!=rhs.level || construction_site!=rhs.construction_site;
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--- src/AIEcho.cpp.orig	2009-08-29 20:39:05 UTC
+++ src/AIEcho.cpp
@@ -4387,7 +4387,7 @@ bool enemy_building_iterator::operator!=(const enemy_b
 {
 	if(is_end && rhs.is_end)
 		return false;
-	return is_end!=rhs.is_end || team!=rhs.team || building_type!=rhs.building_type || level!=rhs.level || construction_site!=rhs.construction_site;
+	return bool(is_end!=rhs.is_end || team!=rhs.team || building_type!=rhs.building_type || level!=rhs.level || construction_site!=rhs.construction_site);
 }