is.get(c1); is.get(c2); is.get(c3); is.get(c4);
if (c1 != 'G' || c2 != 'A' || c3 != 'R' || c4 != 'C')
throw (std::runtime_error("not a GiNaC archive (signature not found)"));
is.get(c1); is.get(c2); is.get(c3); is.get(c4);
if (c1 != 'G' || c2 != 'A' || c3 != 'R' || c4 != 'C')
throw (std::runtime_error("not a GiNaC archive (signature not found)"));