this is maybe a silly question, but what’s wrong with this:
Blue room is a room. A dog is animal. The description is "a blue dog". a dog is in the blue room. Red room is a room. Blue door is a lockable door. It is locked. The matching key is metal key. A blue door is west of blue room and east of red room. A metal key is under a mat. A mat is a thing. The description of the mat is "A woolen mat." The mat is in the blue room.
The sentence ‘A metal key is under a mat’ appears to say two things are the same - I am reading ‘metal key’ and ‘under a mat’ as two different things, and therefore it makes no sense to say that one is the other