Trace of app([1,2,3],A,[1,2,3,4])
T Call:(7) app([1,2,3], _G235, [1,2,3,4])
T Call:(8) app([2,3], _G235, [2,3,4])
T Call:(9) app([3], _G235, [3,4])
T Call:(10) app([], _G235, [4])
T Exit:(10) app([], [4], [4])
T Exit:(9) app([3], [4], [3,4])
T Exit:(8) app([2, ], [4], [2,3,4])
T Exit:(7) app([1,2,3], [4], [1,2,3,4])