I think this position is easier than it looks like and more when you only have to check the king. What about Rc3 attaking the Queen? If black take on c2:
Rc2 Qxc2
Bd8+ g5
Ba5 (Threatening checkmate on e1) Qf2
Bc7 (Threatening checkmate on g3) Zugzwang!
The Queen cannot move from the second row and has to defend the diagonal e1 - h4
Your solution looks good! (1....Rc2 first, Rc3 is an impossible move). If Black plays 1...Qb8+ (instead of Qxc2), then 2.Bc7 - Qb3 3. Bd8+g5 4. Rc4 - Qxc4 and 5. g3 mate. But I think you found the key ideas.
I think this position is easier than it looks like and more when you only have to check the king. What about Rc3 attaking the Queen? If black take on c2:
The Queen cannot move from the second row and has to defend the diagonal e1 - h4
Your solution looks good! (1....Rc2 first, Rc3 is an impossible move). If Black plays 1...Qb8+ (instead of Qxc2), then 2.Bc7 - Qb3 3. Bd8+g5 4. Rc4 - Qxc4 and 5. g3 mate. But I think you found the key ideas.
You are right, thanks :)
That was a very nice variation, too!
What after
4.. Bc7 Qf2
5.. Bd6 zugzwang again
in addition: if Qf4 6.g3!+ then :-) Qxg3 7. Bxg3 check mate.
That's it, very well done! :)
(Sorry for late reply, but I was rather busy during the last hours.)
Great chess problem again, full of hidden quiet moves! :)