diff --git a/build-aux/bootstrap/libprebirth.js b/build-aux/bootstrap/libprebirth.js
index c4556f9..5f32ce3 100644
--- a/build-aux/bootstrap/libprebirth.js
+++ b/build-aux/bootstrap/libprebirth.js
@@ -99,6 +99,10 @@ function $$$p$()
 {
     return argToArr( arguments ).reduce( ( ( x, y ) => x + y ), 0 );
 }
+function $$$_$()
+{
+    return argToArr( arguments ).reduce( ( ( x, y ) => x - y ), 0 );
+}
 
 
 // Node.js stuff