(if
        (not
            (or
                (= ext1 ".LSP"); Autolisp files
                (= ext1 ".VLX"); AutoCAD AutoLISP Macro Application (Autodesk, Inc.)
                (= ext1 ".FAS"); AutoCAD Fast-load Auto LISP (Autodesk, Inc.)
                (= ext1 ".ARX"); ObjectARX files
                (= ext1 ".NRX"); NanoCad module DLL like Arx or Brx
                (= ext1 ".CRX"); Core ObjectARX files
                (= ext1 ".DVB"); VBA files
                (= ext1 ".DBX"); ObjectDBX files
                (= ext1 ".VLS"); ObjectDBX files (ZWCAD analoque format to VLX)
                (= ext1 ".ZELX"); ObjectDBX files (ZWCAD analoque format to FAS)
                (= ext1 ".MNL"); AutoCAD AutoLISP Functions Related to Menu (Autodesk, Inc.)
                (= ext1 ".DES") ;BrisCAD Encryipted Lisp  
               );or
        );not
        (progn
            (princ "\nIts not a path to a Autocad App file")
            (exit)
        );progn 
    );if

.CL=Generic LISP Source Code 
.EL=eMacs Lisp Source Code 
.ELC=eMacs Lisp Byte-compiled Source Code 
.GC1=Golden Common Lisp 1.1 Source Code 
.GC3=Golden Common Lisp 3.1 Source Code 
.KCL=Kyoto Common LISP Source Code 
.L=LISP Program File /LEX Program File 
.LISP=Translators File  of Lisp
.LISPM=Machine File Bitmap for Lisp
.LSP=Program File Lisp
.WKS=XLISP Workspace