[Sadgrinner]

Isn't your answer technically wrong, though?

The sequence is not monotonically increasing. It's strictly increasing. If you test [1, 1, 2] or [1, 1, 1] or [1, 2, 2], you'll get "No" answers even though those sequences are monotonically increasing.

[thaumasiotes]

Not so.

http://mathworld.wolfram.com/MonotoneIncreasing.html

[ddlatham]

So.

http://mathworld.wolfram.com/MonotonicFunction.html

https://en.wikipedia.org/wiki/Monotonic_function