diff options
Diffstat (limited to '')
| -rw-r--r-- | backends/hol4/ilistScript.sml | 37 |
1 files changed, 32 insertions, 5 deletions
diff --git a/backends/hol4/ilistScript.sml b/backends/hol4/ilistScript.sml index 3e17dcc8..c871ba04 100644 --- a/backends/hol4/ilistScript.sml +++ b/backends/hol4/ilistScript.sml @@ -26,10 +26,25 @@ val len_def = Define ‘ “index (i : int) [] = EL (Num i) []” *) val index_def = Define ‘ - index (i : int) [] = EL (Num i) [] ∧ index (i : int) (x :: ls) = if i = 0 then x else (if 0 < i then index (i - 1) ls else ARB) ’ +(* We use the following theorem as a rewriting theorem for [index]: it performs + better with the rewritings. + + TODO: we could even write: + if (0 < i) ∨ (i > 0) ∨ ((0 ≤ i ∨ i >= 0) ∧ (i ≠ 0 ∨ 0 ≠ i)) then ... + *) +Theorem index_eq: + (∀x ls. index 0 (x :: ls) = x) ∧ + (∀i x ls. index i (x :: ls) = + if (0 < i) ∨ (0 ≤ i ∧ i ≠ 0) then index (i - 1) ls + else (if i = 0 then x else ARB)) +Proof + rw [index_def] >> fs [] >> + exfalso >> cooper_tac +QED + val update_def = Define ‘ update ([] : 'a list) (i : int) (y : 'a) : 'a list = [] ∧ @@ -37,6 +52,20 @@ val update_def = Define ‘ if i = 0 then y :: ls else (if 0 < i then x :: update ls (i - 1) y else x :: ls) ’ +Theorem update_eq: + (∀i y. update ([] : 'a list) (i : int) (y : 'a) : 'a list = []) ∧ + + (∀x ls y. update (x :: ls) 0 y = y :: ls) ∧ + + (∀x ls i y. + update (x :: ls) i y = + if (0 < i) ∨ (0 ≤ i ∧ i ≠ 0) then x :: update ls (i - 1) y + else if i < 0 then x :: ls else y :: ls) +Proof + rw [update_def] >> fs [] >> + exfalso >> cooper_tac +QED + Theorem len_eq_LENGTH: ∀ls. len ls = &(LENGTH ls) Proof @@ -49,11 +78,9 @@ Theorem index_eq_EL: i < len ls ⇒ index i ls = EL (Num i) ls Proof - Induct_on ‘ls’ >> rpt strip_tac >> fs [len_def, index_def] >> + Induct_on ‘ls’ >> rpt strip_tac >> fs [len_def, index_eq] >- int_tac >> Cases_on ‘i = 0’ >> fs [] >> - (* TODO: automate *) - sg ‘0 < i’ >- cooper_tac >> fs [] >> - Cases_on ‘Num i’ >- (exfalso >> cooper_tac) >> fs [] >> + Cases_on ‘Num i’ >- (int_tac) >> fs [] >> last_assum (qspec_assume ‘i - 1’) >> pop_assum sg_premise_tac >- cooper_tac >> sg ‘n = Num (i - 1)’ >- cooper_tac >> fs [] >> |