decreasing_by.lean.expected.out

decreasing_by.lean:36:0-43:17: error: Could not find a decreasing measure.
The arguments relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
            n m
1) 36:29-43 = ?
2) 36:46-62 ? _
Please use `termination_by` to specify a decreasing measure.
decreasing_by.lean:66:0-73:19: error: Could not find a decreasing measure.
The arguments relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
            n m
1) 66:29-43 = ?
2) 66:46-62 ? _
Please use `termination_by` to specify a decreasing measure.
decreasing_by.lean:81:13-83:3: error: unexpected token 'end'; expected '{' or tactic
decreasing_by.lean:81:0-81:13: error: unsolved goals
n m : Nat
⊢ (invImage (fun x => PSigma.casesOn x fun n m => (n, m)) Prod.instWellFoundedRelationProd).1 ⟨n, dec2 m⟩ ⟨n, m⟩

n m : Nat
⊢ (invImage (fun x => PSigma.casesOn x fun n m => (n, m)) Prod.instWellFoundedRelationProd).1 ⟨dec1 n, 100⟩ ⟨n, m⟩
decreasing_by.lean:91:0-91:22: error: unsolved goals
case a
n m : Nat
⊢ (invImage (fun x => PSigma.casesOn x fun n m => (n, m)) Prod.instWellFoundedRelationProd).1 ⟨n, dec2 m⟩ ⟨n, m⟩

n m : Nat
⊢ (invImage (fun x => PSigma.casesOn x fun n m => (n, m)) Prod.instWellFoundedRelationProd).1 ⟨dec1 n, 100⟩ ⟨n, m⟩
decreasing_by.lean:99:0-100:22: error: Could not find a decreasing measure.
The arguments relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
            n m
1) 99:29-43 = ?
2) 99:46-62 ? _
Please use `termination_by` to specify a decreasing measure.
decreasing_by.lean:110:0-113:17: error: unsolved goals
n m : Nat
⊢ (invImage (fun x => PSigma.casesOn x fun n m => (n, m)) Prod.instWellFoundedRelationProd).1 ⟨dec1 n, 100⟩ ⟨n, m⟩
decreasing_by.lean:121:0-125:17: error: Could not find a decreasing measure.
The arguments relate at each recursive call as follows:
(<, ≤, =: relation proved, ? all proofs failed, _: no proof attempted)
             n m
1) 121:29-43 = ?
2) 121:46-62 ? _
Please use `termination_by` to specify a decreasing measure.