Loops with exponent three in all isotopes

It was shown by van Rees [18] that a latin square of order n cannot have more than n(n− 1)/18 latin subsquares of order 3. He conjectured that this bound is only achieved if n is a power of 3. We show that it can only be achieved if n ≡ 3 mod 6. We also state several conditions that are equivalent to achieving the van Rees bound. One of these is that the Cayley table of a loop achieves the van Rees bound if and only if every loop isotope has exponent 3. We call such loops van Rees loops and show that they form an equationally defined variety. We also show that (1) In a van Rees loop, any subloop of index 3 is normal, (2) There are exactly 6 nonassociative van Rees loops of order 27 with a non-trivial nucleus, (3) There is a Steiner quasigroup associated with every van Rees loop and (4) Every Bol loop of exponent 3 is a van Rees loop.