Anyway, while I am here I may as well comment on the puzzle. Perhaps not as difficult as it first looked, my starting point was 18ac (I^(L^S)) which had a unique solution and where L proved to be the misprint. After that progress was fairly steady as I recall. This was a brilliant construction but not a favourite with me – I seemed to spend a lot of time making speculative entries and then dreading coming to an impasse. One notable feature was that the standard preamble instruction that all entries were different was actually required for once – the entry for 27dn could have been 80 or 60 except that 17ac had to be 60.