code: public Set<String> compile(final String _equ) throws Exception
      {
          equ = _equ;
          List<EquPart> tokens = tokenize();
          tokens = negatize(tokens);
          tokens = multiplize(tokens);
          countParameters(tokens);
          rpn = rpnize(tokens);
  
          return gatherVariables(tokens);
      }
docs: <p>
  compile.
  </p>
  
  @param _equ a {@link java.lang.String} object.
  @return a {@link java.util.Set} object.
  @throws java.lang.Exception if any.