minusx0xminussxsyminusxyquot0sy0quotsxsysquotminusxysyappnilyyappaddnxyaddnappxyreversenilnilreverseaddnxappreversexaddnnilshufflenilnilshuffleaddnxaddnshufflereversexconcatleafyyconcatconsuvyconsuconcatvyless_leavesxleaffalseless_leavesleafconswztrueless_leavesconsuvconswzless_leavesconcatuvconcatwzrandxxrandxrandsxtrue0less_leaves2app2add2concat2leaf0shuffle1rand1quot2nil0false0s1reverse100minus2cons2FULL