==== tests/cases/compiler/ambientExternalModuleInAnotherExternalModule.ts (2 errors) ====
    
    class D { }
    export = D;
    
    declare module "ext" {
                   ~~~~~
!!! Ambient external modules cannot be nested in other modules.
        export class C { }
    }
    
    // Cannot resolve this ext module reference
    import ext = require("ext");
                         ~~~~~
!!! Cannot find external module 'ext'.
    var x = ext;