enhance capabilities of history

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currently the back option is very naive as it tracks only the previous state and the current state and back sets the current state to the current state.

this means A -> B -> C (current state is C) and going back twice results in the current state being C again:

1. back C -> B
2. back B -> C

It would be better in this case if going back twice would result in current state A

a history implementation that uses a stack like construct instead of tracking only the current and previous state should be considered.