New numeral grammars.

grammars/prelude/Prelude.gf

@@ -83,6 +83,10 @@ oper
 -- bind together two tokens in the lexer, either obligatorily or optionally
 
   oper 
-    bind : Str -> Str -> Str = \x,y -> x ++ "&+" ++ y ;
-    bindOpt : Str -> Str -> Str = \x,y -> variants {bind x y ; x ++ y} ;
+    glue : Str -> Str -> Str = \x,y -> x ++ BIND ++ y ;
+    glueOpt : Str -> Str -> Str = \x,y -> variants {glue x y ; x ++ y} ;
+    noglueOpt : Str -> Str -> Str = \x,y -> variants {x ++ y ; glue x y} ;
+
+-- this should be hidden, and never changed since it's hardcoded in (un)lexers
+    BIND : Str = "&+" ;
 } ;