...

cxx/mcc_mount_astrom.h

@@ -83,6 +83,10 @@ concept mcc_astrom_engine_c = requires(T t, const T t_const) {
                             std::declval<bool>())
     } -> std::same_as<typename T::engine_err_t>;
 
+    // equation of origins
+    {
+        t.eqOrigins(std::declval<typename T::juldate_t>(), std::declval<typename T::eo_t&>())
+    } -> std::same_as<typename T::engine_err_t>;
 
     /*   atmospheric refraction-related methods   */