admin/LithosAnanake
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

proof/: partially close the dictionary-insertion gap (StarForth_Defining_Words.thy)

Browse Source 
Every prior file in the word-source sweep only ever read the abstract
dictionary table; none modelled insertion. dict_insert_entry now models
the word_id-assignment/dictionary-table/latest_id/word_id_next-counter
portion of vm_create_word (dictionary_management.c:379-470), reusing
word_id_next :: nat -- a field already declared in StarForth_Base.thy but
never previously written by any theory. Applied to :, CREATE, VARIABLE,
CONSTANT (StarForth_Defining_Words.thy) and DEFER (StarForth_Defer_Words.thy)
via forth_*_entry_half definitions, each named to keep visible what's
still not modelled: the TIB name-parse dependency, the DF (data-field)
write each word does afterward, and (for :) vm->compiling_word tracking,
none of which have a vm_state counterpart. Pin-shadow conflicts are
sidestepped via an explicit pinned_conflict :: bool parameter, the same
technique already used for the XT-pop gap elsewhere in this suite.

Full suite (54 theories) verifies green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Robert Allan James
2026-08-14 22:31:26 -04:00
co-authored by Claude Sonnet 5
parent dfdabcc2d7
commit cc46cf83f1
3 changed files with 256 additions and 43 deletions
Download Patch File Download Diff File Expand all files Collapse all files
proof/COVERAGE.md
+12 -4
View File
@@ -70,7 +70,7 @@ library itself is separately covered by `StarForth_Q48_16.thy`).
| `format_words.c` | `StarForth_Format_Words.thy` | 17/19 (`#`/`#S` multi-precision division deferred) |
| `system_words.c` | `StarForth_System_Words.thy` | 10/16 + `(ABORT")` helper |
| `vocabulary_words.c` | `StarForth_Vocabulary_Words.thy` | 1/7 partial (entire subsystem is file-scope statics, see FINDINGS.md §1) |
| `defining_words.c` | `StarForth_Defining_Words.thy` | 4/19 full + 2 guard-only (`:`/`;`) |
| `defining_words.c` | `StarForth_Defining_Words.thy` | 4/19 full + 2 guard-only (`:`/`;`) + 4 entry-creation-half (`:`/CREATE/VARIABLE/CONSTANT, added 2026-08-14) |
| `acl_words.c` | `StarForth_ACL_Words.thy` | 7/12 (5 already covered by the pre-existing `ACL_*.thy` policy theories) |
| `dictionary_heat_diagnostic_words.c` | `StarForth_Dictionary_Heat_Diagnostic_Words.thy` | 4/6 full + 1 partial |
| `physics_freeze_words.c` | `StarForth_Physics_Freeze_Words.thy` | 6/9 |
@@ -81,7 +81,7 @@ library itself is separately covered by `StarForth_Q48_16.thy`).
| `framebuffer_words.c`, `keyboard_words.c` | `StarForth_Framebuffer_Words.thy`, `StarForth_Keyboard_Words.thy` | hosted-build fallback branches fully modelled |
| `scroll_words.c`, `ttf_words.c` | `StarForth_Scroll_Words.thy`, `StarForth_TTF_Words.thy` | sentinel-only — words don't exist on hosted builds at all |
| `lifecycle_words_hosted.c` | `StarForth_Lifecycle_Words_Hosted.thy` | 100% — zero deferred remainder |
| `defer_words.c` | `StarForth_Defer_Words.thy` | modelled, but words are dead (shadowed, see FINDINGS.md §3) |
| `defer_words.c` | `StarForth_Defer_Words.thy` | live (see FINDINGS.md §3 correction); DEFER's entry-creation half modelled (added 2026-08-14) |
| `log_words.c` | `StarForth_Log_Words.thy` | 100% |
| `q48_words.c` | `StarForth_Q48_Words.thy` | 17/23 |
| `inference_words.c` | `StarForth_Inference_Words.thy` | 5 accessors full; rest guard/shape |
@@ -103,8 +103,16 @@ effort on the scale of what's already here:
the abstract `dict_entry` model is word-id-indexed, not addressed; no
independent `dsp` register exists to model `SP@`/`SP!` against either.
- **Dictionary insertion** (`vm_create_word`, used by `:`, CREATE, VARIABLE,
CONSTANT, DEFER) — every other file only ever *reads* the abstract
dictionary table; no insertion operation has ever been modelled.
CONSTANT, DEFER) — **partially closed 2026-08-14.** `dict_insert_entry`
(`StarForth_Defining_Words.thy`) now models the word_id-assignment/
dictionary-table/`latest_id`/`word_id_next`-counter portion, reused by
all five words' `forth_*_entry_half` definitions. Still not modelled:
the name parse (TIB gap, same as everywhere else in this suite),
`vm->compiling_word` tracking (no vm_state field), the data-field (DF)
write each of the five words does afterward (still gap (b) below), and
the pin-shadow name-scan guard (sidestepped via an explicit
`pinned_conflict :: bool` parameter, same technique as the XT-pop gap
elsewhere in this suite).
- **The vocabulary chain mechanics** (VOCABULARY/DEFINITIONS/CONTEXT/CURRENT/
FORTH) — file-scope statics, see FINDINGS.md §1, instance #5.
- **The hot-words cache** (`physics_benchmark_words.c`) and **the bucket/
proof/StarForth_Defer_Words.thy
+23 -2
View File
@@ -1,5 +1,5 @@
theory StarForth_Defer_Words
imports StarForth_Base
imports StarForth_Base StarForth_Defining_Words
begin
(* =========================================================================
@@ -66,7 +66,28 @@ lemma is_guard_rest_not_modelled: True
query in this model), and the DF store (gap b). See file header.\<close>
by simp
lemma defer_not_modelled: True \<comment> \<open>DEFER: vm_create_word (gap a) + DF zero-init (gap b).\<close>
(* ── DEFER: entry-creation half, gap (a) PARTIALLY CLOSED 2026-08-14 ─────
`word_defer` (src/word_source/defer_words.c:73-101) calls
`vm_create_word(vm, name, len, defer_runtime)` with no extra flags set
afterward -- same shape as StarForth_Defining_Words.thy's CREATE/
VARIABLE/CONSTANT, reusing `dict_insert_entry 0` directly. NOT modelled:
the name parse (TIB gap), and the DF zero-init that follows (gap b). *)
definition forth_defer_entry_half :: "bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"forth_defer_entry_half pinned_conflict vm = dict_insert_entry 0 pinned_conflict vm"
lemma defer_entry_half_populates_dictionary:
assumes "\<not> pinned_conflict"
shows "\<exists>e. dictionary (forth_defer_entry_half pinned_conflict vm) (word_id_next vm) = Some e
\<and> de_flags e = 0"
using assms by (simp add: forth_defer_entry_half_def dict_insert_entry_def Let_def)
lemma defer_entry_half_pinned_conflict_errors:
assumes "pinned_conflict"
shows "vm_error (forth_defer_entry_half pinned_conflict vm)"
using assms by (simp add: forth_defer_entry_half_def dict_insert_entry_def set_error_def)
lemma defer_not_modelled: True \<comment> \<open>DEFER beyond the entry-creation half: name parse (TIB gap) + DF zero-init (gap b). See forth_defer_entry_half above for what IS now modelled.\<close>
by simp
lemma defer_runtime_not_modelled: True \<comment> \<open>defer_runtime: DF read (gap b) + call-through (gap c).\<close>
by simp
proof/StarForth_Defining_Words.thy
+221 -37
View File
@@ -1,5 +1,5 @@
theory StarForth_Defining_Words
imports StarForth_Base StarForth_Memory_Words
imports StarForth_Base StarForth_Memory_Words ACL_Pin_Monotone
begin
(* =========================================================================
@@ -38,35 +38,47 @@ begin
provable against `vm_mode`/`state_addr`/`memory`/`dictionary`/
`latest_id`.
2. `:` / `;` -- guard conditions modelled; `:`'s STATE/mode-setting half
of `vm_enter_compile_mode` is modelled (identical shape to `]`), but
the dictionary-entry-creation half (`vm_create_word` -> a fresh
DictEntry with `vm->compiling_word` tracking it) is NOT modelled --
see the finding below. `;`'s entire effect beyond the guard
(`vm_exit_compile_mode`: find/compile EXIT, clear WORD_SMUDGED, set
WORD_COMPILED, evict hot-words cache) is NOT modelled for the same
reason plus dependence on the hot-words cache, itself never modelled
in this suite.
3. Everything else (CREATE, VARIABLE, CONSTANT, FORGET, COMPILE,
[COMPILE], LIT, LITERAL, does_rt, DOES>, DEFER, IS, DEFER@, and the
three defining-runtime functions CREATE/VARIABLE/CONSTANT install) --
NOT modelled. Each hits one or more of the same three model gaps,
named once here rather than repeated per word:
of `vm_enter_compile_mode` is modelled (identical shape to `]`), AND
(added 2026-08-14, see `dict_insert_entry` below) its dictionary-
entry-creation half is now PARTIALLY modelled too
(`forth_colon_entry_half`: fresh word_id, WORD_SMUDGED flag, ACL
defaults) -- what remains unmodelled is named at that definition's
site. `;`'s entire effect beyond the guard (`vm_exit_compile_mode`:
find/compile EXIT, clear WORD_SMUDGED, set WORD_COMPILED, evict
hot-words cache) is still NOT modelled, for the same reason plus
dependence on the hot-words cache, itself never modelled in this
suite.
3. Everything else (CREATE, VARIABLE, CONSTANT partially modelled as of
2026-08-14, see below; FORGET, COMPILE, [COMPILE], LIT, LITERAL,
does_rt, DOES>, DEFER, IS, DEFER@, and the three defining-runtime
functions CREATE/VARIABLE/CONSTANT install still NOT modelled) --
each hits one or more of the same three model gaps, named once here
rather than repeated per word:
(a) DICTIONARY-ENTRY CREATION is not modelled anywhere in this proof
suite. `dictionary :: nat \<Rightarrow> dict_entry option` (StarForth_
Base.thy:498) is treated as a fixed, pre-populated table by every
theory so far -- FIND/TRAVERSE/etc. in StarForth_Dictionary_
Manipulation_Words.thy only READ it. This is the first file in
the sweep whose primary job IS insertion (`:`, CREATE, VARIABLE,
CONSTANT, DEFER all call `vm_create_word`). `vm_create_word`
itself parses no input (name arrives pre-parsed) but allocates a
new DictEntry, links it into `vm->latest`, and returns a raw
`DictEntry*` the caller mutates directly (`entry->flags |=
WORD_SMUDGED`, etc.) -- none of which has a counterpart in the
word_id-indexed abstract model with no live pointer aliasing.
This is a materially bigger gap than the raw-pointer-navigation
gap already flagged in dictionary_manipulation_words.c (which
only reads), and is the single largest finding of this file.
(a) DICTIONARY-ENTRY CREATION, PARTIALLY CLOSED 2026-08-14. Was not
modelled anywhere in this proof suite: `dictionary :: nat \<Rightarrow>
dict_entry option` (StarForth_Base.thy:498) was treated as a
fixed, pre-populated table by every theory so far -- FIND/
TRAVERSE/etc. in StarForth_Dictionary_Manipulation_Words.thy
only READ it. This was the first file in the sweep whose primary
job IS insertion (`:`, CREATE, VARIABLE, CONSTANT, DEFER all
call `vm_create_word`). `dict_insert_entry` (defined below) now
models the word_id-assignment/dictionary-table/latest_id/
`word_id_next`-counter portion of `vm_create_word`, reusing the
`word_id_next :: nat` field already declared in StarForth_
Base.thy but never previously written by any theory. What
remains unmodelled per word: `vm_create_word` itself parses no
input (name arrives pre-parsed, but the parse producing that
name is the TIB/input-subsystem gap, present throughout this
suite), does not capture the entry into any per-VM
`vm->compiling_word`-style tracking field (none exists in
vm_state), and callers still mutate the returned `DictEntry*`
directly afterward for flags beyond what `dict_insert_entry`'s
`init_flags` parameter already captures. This is still a
materially bigger gap than the raw-pointer-navigation gap
already flagged in dictionary_manipulation_words.c (which only
reads), even partially closed -- the single largest finding of
this file remains real, just smaller than before.
(b) DATA-FIELD (DF) ADDRESSING: `dict_entry` (StarForth_Base.thy:293)
has no field corresponding to a DictEntry's data-field cell (the
@@ -97,6 +109,88 @@ begin
======================================================================== *)
definition WORD_IMMEDIATE :: nat where "WORD_IMMEDIATE = 0x80"
definition WORD_SMUDGED :: nat where "WORD_SMUDGED = 0x20"
(* ── Dictionary-entry insertion (gap (a), PARTIALLY CLOSED 2026-08-14) ────
`word_id_next` (StarForth_Base.thy, declared but never written by any
theory before this one -- confirmed by grep) is exactly C's
`vm->next_word_id`/`vm_dictionary_acquire_word_id` mechanism
(src/dictionary_management.c:87-92,94-110): a monotonically increasing
counter, one per fresh word, capped at DICTIONARY_SIZE. `vm_create_word`
itself (dictionary_management.c:379-470) does three things this
definition models and one it does not:
1. Pin-shadow guard: scans vm->latest's linked list for a same-name
PINNED entry; refuses (vm->error=1) if found. Sidestepped the same
way StarForth_ACL_Words.thy/StarForth_Physics_Freeze_Words.thy
sidestep the equivalent FIND-shaped dependency: parameterised over
an explicit `pinned_conflict :: bool`, standing in for "whatever a
real name-scan would have found."
2. Allocates a `word_id` via the counter and installs the new entry
into the word-id-indexed table (`vm->word_id_map` / this model's
`dictionary`) -- modelled exactly, both are word_id-indexed.
3. Prepends to `vm->latest`'s linked list, which is also what backs
`latest_id` in this model.
NOT modelled: the real `entry->func` (word_table -- a fixed,
uninterpreted global per StarForth_Base.thy's design, cannot express a
NEW word's dispatch target, which is gap (c)), the physics-metadata
seed (`physics_metadata_init`/`apply_seed` -- modelled as all-zero
`dict_physics`, not the real seeding logic), and the DF cell (gap (b),
unchanged). ACL fields are modelled exactly from the C's literal
initializers (acl_ttl=0, acl_allow=True, acl_mode=ACL_MODE_TTL=0,
acl_pinned=False) -- src/dictionary_management.c:427-430. *)
definition dict_insert_entry :: "nat \<Rightarrow> bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"dict_insert_entry init_flags pinned_conflict vm =
(if pinned_conflict
then set_error vm
else
let wid = word_id_next vm;
e = \<lparr>de_name = '''', de_flags = init_flags, de_heat = 0,
de_word_id = wid,
de_physics = \<lparr>dp_temperature_q8 = 0, dp_last_active_ns = 0,
dp_last_decay_ns = 0, dp_mass_bytes = 0,
dp_avg_latency_ns = 0, dp_state_flags = 0\<rparr>,
de_acl_ttl = 0, de_acl_allow = True, de_acl_mode = ACL_MODE_TTL,
de_acl_pinned = False\<rparr>
in vm\<lparr>dictionary := (dictionary vm)(wid := Some e),
latest_id := Some wid,
word_id_next := wid + 1\<rparr>)"
lemma dict_insert_entry_pinned_conflict_errors:
assumes "pinned_conflict"
shows "vm_error (dict_insert_entry init_flags pinned_conflict vm)"
by (simp add: dict_insert_entry_def set_error_def assms)
lemma dict_insert_entry_assigns_fresh_word_id:
assumes "\<not> pinned_conflict"
shows "latest_id (dict_insert_entry init_flags pinned_conflict vm) = Some (word_id_next vm)"
using assms by (simp add: dict_insert_entry_def Let_def)
lemma dict_insert_entry_populates_dictionary:
assumes "\<not> pinned_conflict"
shows "\<exists>e. dictionary (dict_insert_entry init_flags pinned_conflict vm) (word_id_next vm) = Some e
\<and> de_word_id e = word_id_next vm \<and> de_flags e = init_flags \<and> de_heat e = 0
\<and> de_acl_ttl e = 0 \<and> de_acl_allow e \<and> de_acl_mode e = ACL_MODE_TTL \<and> \<not> de_acl_pinned e"
using assms by (simp add: dict_insert_entry_def Let_def)
lemma dict_insert_entry_advances_counter:
assumes "\<not> pinned_conflict"
shows "word_id_next (dict_insert_entry init_flags pinned_conflict vm) = word_id_next vm + 1"
using assms by (simp add: dict_insert_entry_def Let_def)
lemma dict_insert_entry_data_stack_unchanged:
"data_stack (dict_insert_entry init_flags pinned_conflict vm) = data_stack vm"
by (simp add: dict_insert_entry_def set_error_def Let_def)
lemma dict_insert_entry_not_full_word_id_next_bound: True
\<comment> \<open>NOT modelled: the C's `word_id_next >= DICTIONARY_SIZE` exhaustion
branch (dictionary_management.c:87-91,102), which returns
WORD_ID_INVALID and skips the `word_id_map` write while the linked-
list prepend to vm->latest still happens unconditionally regardless.
This model always succeeds at installing into `dictionary` once past
the pin guard -- a real, uncovered edge case (a VM that defines more
than DICTIONARY_SIZE words), not claimed to be handled.\<close>
by simp
(* ── [ ( -- ) : interpret mode, LIVE version (see file header) ──────────── *)
(* C: vm_store_cell(vm, vm->state_addr, 0); vm->mode = MODE_INTERPRET. *)
@@ -273,6 +367,44 @@ lemma colon_guard_not_full_colon: True
file header finding (a)/(b). Named so the omission is greppable.\<close>
by simp
(* ── : entry-creation half, gap (a) PARTIALLY CLOSED 2026-08-14 ──────────
`vm_enter_compile_mode` (src/vm.c:232-264) does forth_colon_guard's
mode/state effect FIRST, then `vm_create_word(...)`, then
`de->flags |= WORD_SMUDGED` on the fresh entry (vm.c:251) -- unlike
CREATE/VARIABLE/CONSTANT, `:` sets a real flag at creation time, so
this reuses `dict_insert_entry WORD_SMUDGED` rather than
`dict_insert_entry 0`. Composed after forth_colon_guard: only valid
when the nested-`:` guard did not already error (real C: vm_create_word
is never reached if `defining_word_colon`'s own nested check fired,
since that returns before calling vm_enter_compile_mode at all). Still
NOT modelled beyond this: name parse, `vm->compiling_word` tracking
(no vm_state counterpart -- would need a new field, not attempted
here), vm_align+HERE capture, and the DF write of the threaded-body
start address (gap b). *)
definition forth_colon_entry_half :: "bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"forth_colon_entry_half pinned_conflict vm =
dict_insert_entry WORD_SMUDGED pinned_conflict (forth_colon_guard vm)"
lemma colon_entry_half_requires_guard_to_pass:
assumes "vm_mode vm \<noteq> ModeCompile" "\<not> pinned_conflict"
shows "\<exists>e. dictionary (forth_colon_entry_half pinned_conflict vm) (word_id_next (forth_colon_guard vm)) = Some e
\<and> de_flags e = WORD_SMUDGED"
using assms by (simp add: forth_colon_entry_half_def forth_colon_guard_def
dict_insert_entry_def Let_def)
lemma colon_entry_half_still_compile_mode:
assumes "vm_mode vm \<noteq> ModeCompile" "\<not> pinned_conflict"
shows "vm_mode (forth_colon_entry_half pinned_conflict vm) = ModeCompile"
using assms by (simp add: forth_colon_entry_half_def forth_colon_guard_def
dict_insert_entry_def Let_def)
lemma colon_entry_half_not_full_colon: True
\<comment> \<open>Still NOT modelled: name parse, vm->compiling_word tracking (no
vm_state field), vm_align+HERE capture, DF write of the threaded-body
start address (gap b). See section header.\<close>
by simp
(* ── ; ( -- ) : compile-mode guard only ──────────────────────────────────── *)
(* C: error unless vm->mode == MODE_COMPILE; else calls vm_exit_compile_mode,
entirely unmodelled (finds/compiles EXIT, flips WORD_SMUDGED/WORD_COMPILED,
@@ -295,18 +427,70 @@ lemma semicolon_guard_not_full_semicolon: True
counterpart in this suite's abstract model.\<close>
by simp
(* ── Everything else in this file -- NOT MODELLED ─────────────────────────
See file header findings (a) dictionary-entry creation, (b) data-field
addressing, (c) mutable per-entry dispatch. One sentinel lemma per word/
helper, matching the StarForth_Dictionary_Manipulation_Words.thy
convention. *)
(* ── CREATE / VARIABLE / CONSTANT: entry-creation half only, gap (a)
PARTIALLY CLOSED 2026-08-14 ─────────────────────────────────────────────
All three call `vm_create_word(vm, namebuf, nlen, <their own runtime>)`
with no extra flags set afterward (`entry->flags = 0` inside
vm_create_word is the final value) -- so their entry-creation half is
exactly `dict_insert_entry 0`, reused verbatim from the definition
above. NOT modelled, same as before: the name parse that produces
`namebuf`/`nlen` (TIB/input-subsystem gap, present in every word in
this suite that parses a name), CREATE's/VARIABLE's `vm_align`+HERE
capture, VARIABLE's `vm_allot` of one cell, and all three words' DF
write of their respective captured/popped value (gap (b), unchanged).
These are named `forth_<word>_entry_half` deliberately, not
`forth_<word>`, to keep the omission visible at the call site the way
`forth_colon_guard` already does for `:`. *)
lemma create_not_modelled: True \<comment> \<open>CREATE: vm_create_word (gap a) + DF write of captured DFA (gap b).\<close>
definition forth_create_entry_half :: "bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"forth_create_entry_half pinned_conflict vm = dict_insert_entry 0 pinned_conflict vm"
definition forth_variable_entry_half :: "bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"forth_variable_entry_half pinned_conflict vm = dict_insert_entry 0 pinned_conflict vm"
definition forth_constant_entry_half :: "bool \<Rightarrow> vm_state \<Rightarrow> vm_state" where
"forth_constant_entry_half pinned_conflict vm = dict_insert_entry 0 pinned_conflict vm"
lemma create_entry_half_populates_dictionary:
assumes "\<not> pinned_conflict"
shows "\<exists>e. dictionary (forth_create_entry_half pinned_conflict vm) (word_id_next vm) = Some e
\<and> de_flags e = 0"
using assms by (simp add: forth_create_entry_half_def dict_insert_entry_def Let_def)
lemma variable_entry_half_populates_dictionary:
assumes "\<not> pinned_conflict"
shows "\<exists>e. dictionary (forth_variable_entry_half pinned_conflict vm) (word_id_next vm) = Some e
\<and> de_flags e = 0"
using assms by (simp add: forth_variable_entry_half_def dict_insert_entry_def Let_def)
lemma constant_entry_half_populates_dictionary:
assumes "\<not> pinned_conflict"
shows "\<exists>e. dictionary (forth_constant_entry_half pinned_conflict vm) (word_id_next vm) = Some e
\<and> de_flags e = 0"
using assms by (simp add: forth_constant_entry_half_def dict_insert_entry_def Let_def)
lemma create_entry_half_pinned_conflict_errors:
assumes "pinned_conflict"
shows "vm_error (forth_create_entry_half pinned_conflict vm)"
using assms by (simp add: forth_create_entry_half_def dict_insert_entry_def set_error_def)
lemma create_entry_half_not_full_create: True
\<comment> \<open>Still NOT modelled beyond entry creation: name parse, vm_align+HERE
capture, and the DF write of the DFA (gap b). See section header.\<close>
by simp
lemma variable_not_modelled: True \<comment> \<open>VARIABLE: vm_allot + vm_create_word (gap a) + DF write of the cell's address (gap b).\<close>
lemma variable_entry_half_not_full_variable: True
\<comment> \<open>Still NOT modelled beyond entry creation: name parse, vm_align+HERE
capture, vm_allot of one cell, and the DF write of that cell's
address (gap b). See section header.\<close>
by simp
lemma constant_not_modelled: True \<comment> \<open>CONSTANT: vm_create_word (gap a) + DF write of the popped value (gap b).\<close>
lemma constant_entry_half_not_full_constant: True
\<comment> \<open>Still NOT modelled beyond entry creation: name parse, the value pop
(this word's one real vm_state-only guard, `vm->dsp < 0`, is itself
also unmodelled here since it gates the parse that must happen
before vm_create_word), and the DF write of the popped value
(gap b). See section header.\<close>
by simp
lemma create_runtime_not_modelled: True \<comment> \<open>defining_runtime_create: reads current_executing_entry's DF cell (gap b).\<close>
by simp
lemma variable_runtime_not_modelled: True \<comment> \<open>defining_runtime_variable: reads current_executing_entry's DF cell (gap b).\<close>