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Why does using defpackage result in NAME-CONFLICT?

So, I practice lisp with Project Euler, and I put small utility functions in a separate file to reduce duplication, and I expect it to become quite huge, so I went ahead and made a package definition. Here is a compressed version of the file that still illustrates my problem:

(defpackage :euler-util
    (:use :common-lisp)
    (:export :divisible-by))

(in-package :euler-util)

(defun divisible-by (x y)
    (equal 0 (mod x y)))

I can compile and load (Cc Ck) this file in SLIME without any warnings or errors. Now when I use it in another file, I do the following:

(load "util.lisp")
(use-package :euler-util)

(defun euler-1 ()
    (loop for i from 3 to 999 when (or (divisible-by i 3) (divisible-by i 5)) sum i))

When I try to compile and download the THAT file, I get this error:

"USE-PACKAGE # causes name conflicts in # between the following characters: EULER-UTILS: DIVISIBLE-BY, COMMON-LISP -USER :: DIVISIBLE-BY [Condition type NAME-CONFLICT]"

COMMON- LISP -USER ?

+4
2

compile-file , eval-when. util.lisp , ( cl-user). use-package - , , , .

, load use-package eval-when, .

(eval-when (:compile-toplevel :load-toplevel :execute)
  (load "util.lisp")
  (use-package :euler))

, :

(defpackage #:euler
  (:use #:cl #:euler-util))

(in-package #:euler)

, eval-when.

CL , , in-package .

ASDF . :

;;;; my-project.asd

(asdf:defsystem my-project
  :serial t
  :components ((:file "util")
               (:file "my-project")))

- ASDF, (asdf:load-system "my-project") .

Quicklisp, - ~/quicklisp/local-projects/, (ql:quickload "my-project") .

+6

. , , "" . . - , use-package , . , load , , OP cl-user::divisble-by. , , , OP.

:

util.lisp file2.lisp:

$ cat util.lisp 
(defpackage :euler-util
    (:use :common-lisp)
    (:export :divisible-by))

(in-package :euler-util)

(defun divisible-by (x y)
    (equal 0 (mod x y)))

$ cat file2.lisp 
(load "util.lisp")
(use-package :euler-util)

(defun euler-1 ()
    (loop for i from 3 to 999 when (or (divisible-by i 3) (divisible-by i 5)) sum i))

: - "DIVISIBLE-BY" CL-USER, , , :

$ sbcl --noinform
* (defun divisible-by (&rest args) (declare (ignore args)))

DIVISIBLE-BY
* (load "file2")

debugger invoked on a NAME-CONFLICT in thread #<THREAD "initial thread" RUNNING
                                                 {1002979041}>:
  USE-PACKAGE #<PACKAGE "EULER-UTIL"> causes name-conflicts in
  #<PACKAGE "COMMON-LISP-USER"> between the following symbols:
    EULER-UTIL:DIVISIBLE-BY, COMMON-LISP-USER::DIVISIBLE-BY
See also:
  The ANSI Standard, Section 11.1.1.2.5

Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [RESOLVE-CONFLICT] Resolve conflict.
  1: [RETRY           ] Retry EVAL of current toplevel form.
  2: [CONTINUE        ] Ignore error and continue loading file "…/file2.lisp".
  3: [ABORT           ] Abort loading file "…/file2.lisp".
  4:                    Exit debugger, returning to top level.

(NAME-CONFLICT
 #<PACKAGE "COMMON-LISP-USER">
 USE-PACKAGE
 #<PACKAGE "EULER-UTIL">
 EULER-UTIL:DIVISIBLE-BY
 DIVISIBLE-BY)

, . SBCL , ( ) SLIME. . , : --noinform ; --eval "'divisible-by" cl-user:divisible-by; --load file2.lisp . , , .

$ sbcl --noinform --eval "'divisible-by" --load file2.lisp 

debugger invoked on a NAME-CONFLICT in thread #<THREAD "initial thread" RUNNING
                                                 {1002979311}>:
  USE-PACKAGE #<PACKAGE "EULER-UTIL"> causes name-conflicts in
  #<PACKAGE "COMMON-LISP-USER"> between the following symbols:
    EULER-UTIL:DIVISIBLE-BY, COMMON-LISP-USER::DIVISIBLE-BY
See also:
  The ANSI Standard, Section 11.1.1.2.5

Type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [RESOLVE-CONFLICT] Resolve conflict.
  1: [RETRY           ] Retry EVAL of current toplevel form.
  2: [CONTINUE        ] Ignore error and continue loading file "/home/taylorj/tmp/package-issue/file2.lisp".
  3: [ABORT           ] Abort loading file "/home/taylorj/tmp/package-issue/file2.lisp".
  4:                    Ignore runtime option --load "file2.lisp".
  5:                    Skip rest of --eval and --load options.
  6:                    Skip to toplevel READ/EVAL/PRINT loop.
  7: [QUIT            ] Quit SBCL (calling #'QUIT, killing the process).

(NAME-CONFLICT
 #<PACKAGE "COMMON-LISP-USER">
 USE-PACKAGE
 #<PACKAGE "EULER-UTIL">
 EULER-UTIL:DIVISIBLE-BY
 DIVISIBLE-BY)

0, :

0] 0

Select a symbol to be made accessible in package COMMON-LISP-USER:
  1. EULER-UTIL:DIVISIBLE-BY
  2. COMMON-LISP-USER::DIVISIBLE-BY

Enter an integer (between 1 and 2): 1

euler-util:divisible-by , CL-USER, , :

* (euler-1)

233168

.

, , , , , , . , (, , "DIVISIBLE-BY" CL-USER. Lisp :

$ sbcl --load file2.lisp --noinform 
* (euler-1)

233168
0

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