Lit.Core: prevent users from defining type named "U64"

base/Lit/Core.kind

@@ -447,7 +447,11 @@ Lit.Core.World.run.statement(
             data: 
               log("- new_type: " | type.name)
               case world{type.name} as got_type {
-                none: some(world{type.name} <- Lit.Core.Entry.type(type))
+                none:
+                  if not(type.name =? "U64") then
+                    some(world{type.name} <- Lit.Core.Entry.type(type))
+                  else
+                    log("error: cannot redefine built-in type named 'U64'") none
               } default log("error: type redefinition: " | type.name) none
           }
         bond:
@@ -623,7 +627,13 @@ Lit.Core.World.run.terms(
 // -----
 Lit.Core: _
   let world = {}
-  let code = Lit.Lang.Type|Lit.Lang.Cmp|Lit.Lang.Nat|Lit.Lang.Bits|Lit.Lang.BitsMap|`
+  let code = 
+    Lit.Lang.Type
+    | Lit.Lang.Cmp
+    | Lit.Lang.Nat
+    | Lit.Lang.Bits
+    | Lit.Lang.BitsMap
+    |`
 type BoolList {
   nil
   cons{

base/Lit/Lang/BitsMap.kind

@@ -156,7 +156,7 @@ BitsMap.transct_2(state: BitsMap, from: Bits, to: Bits, sum: Bits): BitsMap
                       //[[dando um set]]
                       
                       //alterar o valor do receiver (adicionar o sum )
-                      [[dando um set ]]
+                      // [[dando um set ]]
 //                  call 
 //                  state
 //                false:

base/Lit/Lang/Type.kind

@@ -67,4 +67,6 @@ type BitsBitsBits {
     snd: Bits
     trd: Bits
   }
+}
+
 `