The leaf node now contains just 7.
Repair strategy: try to borrow values from a neighbouring node.
We join together the current node and a neighbour to form a combined node.
Don't forget to include the value between these 2 adjacent subtrees.
We choose to join [7] with [17,22,44,45]:
[6,7,10,17,22,44,45]
We distinguish 2 cases, depending on whether the neighbour contributes exactly (M-1)/2 values or more.