I<r> may be the same B<BIGNUM> as I<a> or I<b>.
BN_sub() subtracts I<b> from I<a> and places the result in I<r> (C<r=a-b>).
+I<r> may be the same B<BIGNUM> as I<a> or I<b>.
BN_mul() multiplies I<a> and I<b> and places the result in I<r> (C<r=a*b>).
I<r> may be the same B<BIGNUM> as I<a> or I<b>.
L<bn(3)>, L<ERR_get_error(3)>, L<BN_CTX_new(3)>,
L<BN_add_word(3)>, L<BN_set_bit(3)>
+=head1 COPYRIGHT
+
+Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (the "License"). You may not use
+this file except in compliance with the License. You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
=cut