I have a list of 3D points, and I'd like to run a Predict on them just to test. It should be fairly straightforward. Here's a simple example:

trains = {{1, 2, 3} -> {4, 5, 6}, {2, 3, 4} -> {7, 8, 9}};

p = Predict[trains];

ERROR:
Predict: Incompatible variable type (Numerical) and variable value ({4,5,6}).

I'm not sure what I'm doing wrong. Any advise?