Claude 3 Opus just did fine for me using the original problem statement as well:
No, it is not possible to make a stack with block A on top of block B and block B on top of block C without moving block C. Here’s why:
Initially, block C is on top of block A, and block B is separate on the table.
To get block B on top of block C, you would need to move block C to place block B underneath it. However, the question specifically states that you cannot move block C.
Since block C cannot be moved, it is impossible to place block B between block C and block A.
Therefore, given the initial arrangement and the constraint of not moving block C, it is not possible to achieve the desired stack of blocks with A on top of B, and B on top of C.
[edited to show the temperature-0 response rather than the previous (& also correct) temperature-0.7 response, for better reproducibility]
Claude 3 Opus just did fine for me using the original problem statement as well:
[edited to show the temperature-0 response rather than the previous (& also correct) temperature-0.7 response, for better reproducibility]