Inferred termination measure:
termination_by n - i
Inferred termination measure:
termination_by xs.size - i
Inferred termination measure:
termination_by xs.size - i
Inferred termination measure:
termination_by (xs.size - i, ys.size - j)
Inferred termination measure:
termination_by (xs.size - i, i - j)
Inferred termination measure:
termination_by (xs.size - i, i)
guessLexDiff.lean:84:4-84:11: error: fail to show termination for
  failure
with errors
failed to infer structural recursion:
Not considering parameter xs of failure:
  it is unchanged in the recursive calls
Cannot use parameter i:
  failed to eliminate recursive application
    _root_.failure xs i


Could not find a decreasing measure.
The basic measures relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
            i #1 #2 i + 1 0 - i #3 i + i
1) 85:26-38 =  =  =     =     =  =     =
2) 85:58-76 ?  <  _     _     _  _     _
3) 85:26-38 =  =  =     =     =  =     =
4) 88:26-42 _  <  _     _     _  _     _
5) 88:26-42 ?  ≤  ≤     ?     ≤  ≤     ?
6) 88:26-42 _  <  _     _     _  _     _
7) 88:26-42 _  <  _     _     _  _     _
8) 88:26-42 _  <  _     _     _  _     _
9) 97:8-20  _  <  _     _     _  _     _

#1: xs.size - i
#2: xs.size - (i + 1)
#3: 42 - i

Please use `termination_by` to specify a decreasing measure.
guessLexDiff.lean:102:4-102:18: error: fail to show termination for
  mutual_failure
  mutual_failure2
with errors
failed to infer structural recursion:
Not considering parameter xs of mutual_failure:
  it is unchanged in the recursive calls
Not considering parameter xs of mutual_failure2:
  it is unchanged in the recursive calls
Cannot use parameters i of mutual_failure and i of mutual_failure2:
  failed to eliminate recursive application
    mutual_failure2 xs i


Could not find a decreasing measure.
The basic measures relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
Call from mutual_failure to mutual_failure2 at 104:4-24:
   i #1 #2 i + 1
i  =  ?  ?     <
#3 ?  =  ?     ?
Call from mutual_failure to mutual_failure2 at 104:52-78:
   i #1 #2 i + 1
i  ?  _  _     =
#3 _  <  _     _
Call from mutual_failure to mutual_failure2 at 104:4-24:
   i #1 #2 i + 1
i  _  _  _     <
#3 _  =  _     _
Call from mutual_failure to mutual_failure2 at 111:4-28:
   i #1 #2 i + 1
i  _  _  _     =
#3 _  <  _     _
Call from mutual_failure to mutual_failure2 at 117:8-28:
   i #1 #2 i + 1
i  _  _  _     <
#3 _  ?  _     _
Call from mutual_failure2 to mutual_failure at 123:4-23:
      i #3
i     _  _
#1    _  _
#2    _  _
i + 1 ?  _
Call from mutual_failure2 to mutual_failure at 123:50-75:
      i #3
i     _  _
#1    _  _
#2    _  _
i + 1 _  _
Call from mutual_failure2 to mutual_failure at 127:4-27:
      i #3
i     _  _
#1    _  _
#2    _  _
i + 1 _  _
Call from mutual_failure2 to mutual_failure at 133:8-27:
      i #3
i     _  _
#1    _  _
#2    _  _
i + 1 _  _


#1: xs.size - i
#2: xs.size - (i + 1)
#3: xs.size - i

Please use `termination_by` to specify a decreasing measure.