Two-Four-Tree Remove (given a key k)

    Find the node r that contains the data element (dp) with the given k;
    if (r is not a leaf node) {
        swap <k, dp> with its direct predecessor in node p
        r = p; // r is guaranteed to be a leaf node now
    }
    remove <k, dp> from leaf node r
    r->size--; 
    while (r->size == 0 && r->parent != 0) {
        p = r->parent;
        if (r's left sibling's size >= 2) {
            r->child[1] = r->child[0]
            move p's <key, dataptr> pair before pointer r to node r
            r->child[0] = r's sibling's last subtree 
            move r's siblings last <key, dataptr> pair to parent's emptied spot
            decrease r's sibling's size by 1 // and it won't be 0
            // note that p's size is unchanged
        } else {
            // r's sibling only has one data item
            //     and two subtrees
            // r has just one subtree
            // all three subtree could be empty if r is leaf node
            // but that's OK
            merge p's <key, dataptr> pair before pointer r
                 and r's one subtree into r's left sibling node
            increase r's sibling's size by 1 // it should be 2
            adjust p's entries so that there is no hole in the arrays
            p->size--; // p's size could be 0 now
            delete r;
        }
        r = p; // go one level up to the parent node;
    }

    if (r->size == 0) { // root node becomes empty
        // r still only has at most one subtree
        root = r->child[0];
        delete r;
    }
}