Has anyone completed this? No one has yet posted here or in the Other Place. By considering in turn 3dn, 3ac, 9ac, 10ac, and 8dn (with revisiting), I reach a contradiction, namely that 10ac is either 4*9 or 6*9 and a square: there is no such perfect square. I’ve noted that the reference to the Time Travel department may allow the possibility that the puzzle is from the future, but that doesn’t seem to affect my deductions.