code: private static boolean equalsAsCVE(AbstractExpression e1, AbstractExpression e2) {
          final ConstantValueExpression ce1 = asCVE(e1), ce2 = asCVE(e2);
          return ce1 == null || ce2 == null ? ce1 == ce2 : ce1.equals(ce2);
      }
docs: Check whether two expressions, each either a CVE or PVE, have same content.
  \pre both must be either CVE or PVE.
  @param e1 first expression
  @param e2 second expression
  @return whether their contents match.