[1,2,3,4,5,6,7,8,9]

validation: [1,5,7], training: [2,3,4,6,8,9]
validation: [2,3,6], training: [1,7,4,5,8,9]
validation: [4,8,9], training: [2,3,1,6,4,7]

validation: [2], training: [1,3,4,5,6,7,8,9]
validation: [3], training: [1,2,4,5,6,7,8,9]
validation: [5], training: ...
validation: [4], training: ...
validation: [6], training: ...
validation: [1], training: ...
validation: [7], training: ...
validation: [9], training: ...
validation: [8], training: ...

validation: [1,2,7,8], training: [3,4,5,6,9]
(1 subsample overall)