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Red [ needs: 'view ]

empty: 4x4

grid: random do [
    res: copy[]
    repeat i 15 [append res to string! i]
    res
]

loop 15 [grid: next insert grid 't]

grid: head grid

loop 3 [grid: insert skip grid 8 'return]

grid: head insert [empty-cell: base 50x50 silver ] head grid

view head insert grid [
    title "15 game"
    backdrop silver
    style t: button 50x50 [
        tmp: face/offset
        i: tmp/y / face/size/y + 1
        j: tmp/x / face/size/x + 1
        if  (absolute empty/1 - i) + (absolute empty/2 - j) = 1 [
            face/offset: empty-cell/offset
            empty-cell/offset: tmp
            empty: as-pair i j
        ]
    ]
    across
]