Trace of app([1,2,3],[4],Z)
T Call: ( 7)app([1,2,3], [4], _G191)
T Call: ( 8)app([2,3], [4], _G299)
T Call: ( 9)app([3], [4], _G302)
T Call: (10)app([], [4], _G305)
T Exit: (10)app([], [4], [4])
T Exit: ( 9)app([3], [4], [3,4])
T Exit: ( 8)app([2,3], [4], [2,3,4])
T Exit: ( 7)app([1,2,3], [4], [1,2,3,4])