Hi! I'm enjoying the game, and the puzzles are getting rather difficult.
I'd like to recommend a feature to aid in puzzle solving on screen. Maybe right click to give an indication for whether a lock should be used or not, perhaps represented by a tick/cross or some indication on the corner. With the staggering number of locks on the screen sometimes, tracking the line of logic could be helped with something like this.
Viewing post in Bug Reports / Feature Request!
This is actually already a planned feature for the game! I intend to eventually add pencilmarking by clicking a key/door and assigning a colored number, letter, or other symbol to it to assist the player in solving it. I can't update the demo, so it'll have to be for when the full game is released, but I hope that will be satisfactory.