andtrueXXandfalseYfalseiftrueXYXiffalseXYYadd0XXaddsXYsaddXYfirst0XnilfirstsXconsYZconsYfirstXZfromXconsXfromsXand21true0false0if31add2100s1first212nil0cons2from1FULL./TRS/CSR/Ex15_Luc98.trs