optional<unsigned> is_internal_cases(expr const & e) { return is_internal_symbol(e, *g_cases); }
optional<unsigned> is_internal_proj(expr const & e) { return is_internal_symbol(e, *g_proj); }
// ========= bool Tape::is_valid_symbol (const symbol_t& symbol_i) const { return (is_input_symbol (symbol_i) || is_internal_symbol (symbol_i) || is_empty_symbol (symbol_i)); }