@Override
public String getHeaderField(final String field) {
final List<String> values = headers.get(field);
final StringBuilder sb = new StringBuilder();
for (final String v : values) sb.append(v).append(';');
return sb.substring(0, sb.length() - 1);
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder();
for (final Expr e : preds) sb.append('[').append(e).append(']');
return sb.toString();
}