:: cross-product ( a b -- vec )
    a 31matrix?
    b 31matrix? and not [ a b not-31matrix ]
    [
        {
            [ { 1 0 0 } a b 3append det ]
            [ { 0 1 0 } a b 3append det ]
            [ { 0 0 1 } a b 3append det ]
        } [ call( -- x ) ] map
    ] if ;



:: cross-product ( a b -- vec )
    a 31matrix?
    b 31matrix? and not [ a b not-31matrix ]
    [
        [
            { 1 0 0 } a b 3append det
            { 0 1 0 } a b 3append det
            { 0 0 1 } a b 3append det
        ] output>array
    ] if ;



:: cross-product ( a b -- vec )
    a 31matrix?
    b 31matrix? and not [ a b not-31matrix ]
    [
        { 1 0 0 } a b 3append det
        { 0 1 0 } a b 3append det
        { 0 0 1 } a b 3append det
        3array
    ] if ;



:: cross-product ( a b -- vec )
    a 31matrix?
    b 31matrix? and not [ a b not-31matrix ]
    [
        { { 1 0 0 } { 0 1 0 } { 0 0 1 } } [ a b 3append det ] map
    ] if ;