appappmapfnilnilappappmapfappappconsxxsappappconsappfxappappmapfxsappflattenappappnodexxsappappconsxappconcatappappmapflattenxsappconcatnilnilappconcatappappconsxxsappappappendxappconcatxsappappappendnilxsxsappappappendappappconsxxsysappappconsxappappappendxsysapp2map0nil0cons0flatten0node0concat0append0FULL./TRS/higher-order/Bird/TreeFlatten.trs