* (asdf:load-system :paren-psos)                    

; loading system definition from
; /home/iain/.local/share/common-lisp/source/paren-psos/paren-psos.asd into
; #<PACKAGE "ASDF0">

debugger invoked on a LOAD-SYSTEM-DEFINITION-ERROR in thread #<THREAD
                                                               "initial thread" RUNNING
                                                               {AACA869}>:
  Error while trying to load definition for system paren-psos from pathname
  /home/iain/.local/share/common-lisp/source/paren-psos/paren-psos.asd:
  component "paren-files" not found

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

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

((FLET #:LAMBDA1286) component "paren-files" not found)
source: 
; file: /usr/share/common-lisp/source/cl-asdf/asdf.lisp
(ERROR 'LOAD-SYSTEM-DEFINITION-ERROR :NAME NAME :PATHNAME ON-DISK :CONDITION
       CONDITION)
0]