anchor.diff:  
   # gpg keys listed at https://github.com/nodejs/node#release-team
   RUN set -ex \
  -  && keyservers="hkp://p80.pool.sks-keyservers.net:80 ha.pool.sks-keyservers.net hkps.pool.sks-keyservers.net pool.sks-keyservers.net keyserver.ubuntu.com" \
  +  && keyservers="hkp://p80.pool.sks-keyservers.net:80 hkp://ipv4.pool.sks-keyservers.net hkp://pgp.mit.edu:80" \
     && for key in \
       94AE36675C464D64BAFA68DD7434390BDBE9B9C5 \
       FD3A5288F042B6850C66B31F09FE44734EB7990E \
  
positive.code: ENV YARN_VERSION 1.9.4
  
  RUN set -ex \
    && for key in \
      6A010C5166006599AA17F08146C2130DFD2497F5 \
    ; do \
      gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" || \
      gpg --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
      gpg --keyserver hkp://pgp.mit.edu:80 --recv-keys "$key" ; \
    done \
    && curl -fsSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz" \
    && curl -fsSLO --compressed "https://yarnpkg.com/downloads/$YARN_VERSION/yarn-v$YARN_VERSION.tar.gz.asc" \
  
negative.code:   ; do \
      keyserver_ok=""; \
      for keyserver in ${keyservers}; do \
        gpg --batch --keyserver ${keyserver} --recv-keys "$key"; >/dev/null 2>&1 && keyserver_ok="ok" && break;\
      done; \
      if [ -z "$keyserver_ok" ]; then echo "No valid response from keyservers"; exit 1; fi; \
    done
  