anchor.diff:  
   from petsc as slepc
   
  +ARG SLEPC_VERSION
  +
   USER root
   WORKDIR /opt
   RUN curl --no-progress-meter https://slepc.upv.es/download/distrib/slepc-$SLEPC_VERSION.tar.gz | tar xzf -
  
positive.code: 
  FROM base-${PLATFORM} as build
  
  ARG PETSC_VERSION
  ARG SLEPC_VERSION
  
  # add virtualenvironment to install python packages
  RUN python3 -m venv /venv
  
  
negative.code: 
  
  from build as petsc
  
  ARG PETSC_VERSION
  
  # install PETSc
  USER root
  