Function documentation for aref uses two different names for the same
function argument:

=======================================
(aref ARRAY IDX)
Return the element of ARG at index IDX.
...
=======================================

ARRAY <---> ARG





In GNU Emacs 26.0.91 (build 1, x86_64-apple-darwin17.3.0, NS appkit-1561.20
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 of 2018-01-23 built on kl-13837
Windowing system distributor 'Apple', version 10.3.1561
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C-x <up> is undefined

Configured using:
 'configure --disable-dependency-tracking --disable-silent-rules
 --enable-locallisppath=/usr/local/share/emacs/site-lisp
 --infodir=/usr/local/Cellar/emacs/26.0.91/share/info/emacs
 --prefix=/usr/local/Cellar/emacs/26.0.91 --without-x --with-xml2
 --without-dbus --with-gnutls --with-imagemagick --with-modules
 --with-rsvg --without-pop --with-ns --disable-ns-self-contained'

Configured features:
JPEG RSVG IMAGEMAGICK NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS
NS MODULES LCMS2

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