: det ( matrix -- x )
    dup 33matrix? not [ not-33matrix ]
    [
        {
            [ [ { 0 4 8 } ] dip nths product ]
            [ [ { 1 5 6 } ] dip nths product ]
            [ [ { 2 3 7 } ] dip nths product + + ]
            [ [ { 0 5 7 } ] dip nths product ]
            [ [ { 1 3 8 } ] dip nths product ]
            [ [ { 2 4 6 } ] dip nths product + + - ]
        } cleave
    ] if ;