Periodic Golay pairs of length 72
  We construct supplementary difference sets (SDS) with parameters $(72;36,30;30)$. These SDSs give periodic Golay pairs of length 72. No periodic Golay pair of length 72 was known previously. The smallest undecided order for periodic Golay pairs is now 90. The periodic Golay pairs constructed here are the first examples having length divisible by a prime congruent to 3 modulo 4. The main tool employed is a recently introduced compression method. We observe that Turyn's multiplication of Golay pairs can be also used to multiply a Golay pair and a periodic Golay pair. 
Dragomir Z. Djokovic and Ilias S. Kotsireas
math.CO