title: R does not Recognize that a Package is Installed
body: <p>When I try to use the command <code>library(Seurat)</code>, I get an error telling me &quot;there is no package called ‘pillar’&quot; installed.  However, I <strong>do</strong> have the pillar package installed: I've checked my packages folder multiple times.  The full text of the error is:</p>
  <blockquote>
  <p>Error: package or namespace load failed for ‘Seurat’ in loadNamespace(j &lt;- i[[1L]], c(lib.loc, .libPaths()), versionCheck = vI[[j]]):
  there is no package called ‘pillar’</p>
  </blockquote>
  <p>Furthermore, I've tried downloading pillar again via the command <code>devtools::install_github(&quot;r-lib/pillar&quot;)</code>, but that doesn't seem to work either.  This may be because, every time I try this, it returns the message:</p>
  <pre><code>installing the source package ‘pillar’
  
  trying URL 'https://cran.rstudio.com/src/contrib/pillar_1.4.6.tar.gz'
  Content type 'application/x-gzip' length 113884 bytes (111 KB)
  
  ==================================================
  downloaded 111 KB
  
  dyld: lazy symbol binding failed: Symbol not found: _utimensat
    Referenced from: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libR.dylib (which was built for Mac OS X 10.13)
    Expected in: /usr/lib/libSystem.B.dylib
  
  dyld: Symbol not found: _utimensat
    Referenced from: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libR.dylib (which was built for Mac OS X 10.13)
    Expected in: /usr/lib/libSystem.B.dylib
  
  /Library/Frameworks/R.framework/Resources/bin/INSTALL: line 34:  1816 Done                    echo 'tools:::.install_packages()'
        1817 Abort trap: 6           | R_DEFAULT_PACKAGES= LC_COLLATE=C &quot;${R_HOME}/bin/R&quot; $myArgs --no-echo --args ${args}
  
  **Warning in install.packages :
    installation of package ‘pillar’ had non-zero exit status**
  
  The downloaded source packages are in
      ‘/private/var/folders/r8/9lw5sbl5549_bw2qlv3y24580000gn/T/Rtmpa5vp68/downloaded_packages’
  </code></pre>
  <p><strong>Any help resolving this issue would be immensely appreciated.  Thanks in advance!</strong></p>