{
    /(b_sub)
        (bA)(bB)
            /(zqA)(lbA)(hb!A)
                /
                    /(zqB)(lbB)(hb!B)
                        /
                            /(hsAB)(hsBA)
                                /
                                    /
                                        /
                                            /[hsBA][b_double]
                                        /
                                            /[hsAB][b_double]
                                        [pair]
                                    /
                                        /(zqhsAB)(lbAB-unused)(hb!AB-unused)
                                            /
                                                /
                                                    [b0]
                                                /
                                                    /
                                                        /
                                                            /
                                                                [b1]
                                                            /
                                                                [hsAB]
                                                            [b_sub]
                                                        [first]
                                                    /
                                                        [1]
                                                    [b!]
                                                [pair]
                                            /
                                                /
                                                    /[hsBA]/[1][b!]
                                                /
                                                    [b0]
                                                [pair]
                                            [zqhsAB]
                                        [hsAB]
                                    [lbB]
                                /
                                    /
                                        /(zqhsBA)(lbBA-unused)(hb!BA-unused)
                                            /
                                                /
                                                    /
                                                        /
                                                            /
                                                                [hsBA]
                                                            /
                                                                [b1]
                                                            [b_sub]
                                                        [second]
                                                    /
                                                        [1]
                                                    [b!]
                                                /
                                                    [b0]
                                                [pair]
                                            /
                                                /
                                                    [b0]
                                                /
                                                    /[hsAB]/[1][b!]
                                                [pair]
                                            [zqhsBA]
                                        [hsBA]
                                    /
                                        /
                                            /[hsBA][b_double]
                                        /
                                            /[hsAB][b_double]
                                        [pair]
                                    [lbB]
                                [lbA]
                            /[hb!B]/[hb!A][b_sub]
                        /
                            /
                                [b0]
                            /
                                [bA]
                            [pair]
                        [zqB]
                    [bB]
                /
                    /
                        [bB]
                    /
                        [b0]
                    [pair]
                [zqA]
            [bA]
    [YC]
|
    b_sub
}