+=item B<open_problem>(I<$contest>, I<$problem>, I<$owner>, I<$time>)
+
+Notes that I<$owner> has opened the problem I<$problem> of contest
+I<$contest> at time I<$time>. If the C<opens> table already contains
+this (I<$contest>, I<$problem>, I<$owner>) triplet, this function does
+nothing.
+