qsort
nil
nil
qsort
cons
x
xs
append
qsort
filterlow
last
cons
x
xs
cons
x
xs
cons
last
cons
x
xs
qsort
filterhigh
last
cons
x
xs
cons
x
xs
filterlow
n
nil
nil
filterlow
n
cons
x
xs
if1
ge
n
x
n
x
xs
if1
true
n
x
xs
filterlow
n
xs
if1
false
n
x
xs
cons
x
filterlow
n
xs
filterhigh
n
nil
nil
filterhigh
n
cons
x
xs
if2
ge
x
n
n
x
xs
if2
true
n
x
xs
filterhigh
n
xs
if2
false
n
x
xs
cons
x
filterhigh
n
xs
ge
x
0
true
ge
0
s
x
false
ge
s
x
s
y
ge
x
y
append
nil
ys
ys
append
cons
x
xs
ys
cons
x
append
xs
ys
last
nil
0
last
cons
x
nil
x
last
cons
x
cons
y
xs
last
cons
y
xs
qsort
1
nil
0
cons
2
append
2
filterlow
2
last
1
filterhigh
2
if1
4
ge
2
true
0
false
0
if2
4
0
0
s
1
ys
0
INNERMOST
./AProVE_09_Inductive/qsortlast.trs