Compare commits

...

2 commits

Author SHA1 Message Date
ProgramSnail
adeefc1c87 structures: part of eval rules 2026-04-19 13:13:51 +00:00
ProgramSnail
ac88ca11cf structures: part of semantics (new value) 2026-04-19 11:10:52 +00:00

View file

@ -15,6 +15,8 @@
#h(10pt)
#let rf = $\& #h(3pt)$
#let isCorrect = `isCorrect`
#let isRead = `isRead`
@ -25,13 +27,28 @@
#let isIn = `isIn`
#let isOut = `isOut`
#let readTag = `read`
#let writeTag = `write`
#let copyTag = `copy`
#let inTag = `in`
#let outTag = `out`
#let mode = `mode`
#let Copy = `Copy`
#let Ref = `Ref`
#let MaybeWrite = [$diamond$ `Write`]
#let AlwaysWrite = [$square$ `Write`]
#let Read = `Read`
#let In = `In`
#let Out = `Out`
#let expr = `expr`
#let stmt = `stmt`
#let decl = `decl`
#let prog = `prog`
#let path = `path`
#let type = `type`
#let modedType = `modedtype`
#bnf(
Prod(`read`,
// NOTE: not three modalities for write, because read does not change value
@ -54,7 +71,7 @@
Prod(
`mode`,
{
Or[`read` #h(3pt) `write` #h(3pt) `copy` #h(3pt) `in` #h(3pt) `out`][]
Or[$inTag space outTag$][]
}
),
Prod(
@ -71,33 +88,36 @@
Prod(
`type`,
{
Or[$()$][simple type representing all primitive types] // `Unit`
Or[\& #h(3pt) `mode` #h(3pt) `type`][reference to structure, contains copy / ref choice] // `Ref`
Or[$readTag writeTag ()$][simple type representing all primitive types] // `Unit`
Or[$rf copyTag space type$][reference to structure, contains copy / ref choice] // `Ref`
Or[$[type+]$][tuple type] // `Prod`
// Or[`type` $times$ `type`][pair type, allows to make tuples] // `Prod`
// Or[`type` $+$ `type`][union type (important in some way ???)] // `Sum` // TODO ?
// NOTE: do not use names in type
// Or[$lambda_((x type)+)$][type of lambda or function pointer, defined by function declaration] // `Fun`
Or[$lambda type+$][type of lambda or function pointer, defined by function declaration] // `Fun`
Or[$lambda (modedType)+$][type of lambda or function pointer, defined by function declaration] // `Fun`
}
),
Prod(
`modedtype`,
{
Or[$mode type$][type woth in and out modifiers]
}
),
// FIXME: replace with expr
Prod(
`expr`,
{
Or[$()$][value of simple type] // `Unit`
Or[$path$][value from variable] // `Path`
Or[$\& #h(3pt) expr$][reference expr] // `Ref`
Or[$rf expr$][reference expr] // `Ref`
Or[$[expr+]$][tuple expr] // `Prod`
// NOTE: replaced with simple path value
// Or[$lambda_path$][function value from variable] // `Fun`
}
),
Prod(
`stmt`,
{
Or[`CALL` $f space expr+$][call function]
Or[`CALL` $path space expr+$][call function]
Or[`WRITE` $path$][write to variable]
Or[`READ` $path$][read from variable]
Or[$stmt ; stmt$][control flow operator, xecution ]
@ -109,7 +129,7 @@
{
// TODO: path not allowed ??
Or[$"var" X : type = expr$][global variable declaration]
Or[$"fun" X ((X : type)+) = stmt$][function declaration]
Or[$"fun" X ((X : modedType)+) = stmt$][function declaration]
}
),
Prod(
@ -122,21 +142,19 @@
== Value Model
#let rf = $\& #h(3pt)$
// FIXME: check & add details
#let deepvalue = `deepvalue`
#let deepValue = `deepvalue`
#let value = `value`
#bnf(
Prod(
$deepvalue$,
$deepValue$,
{
Or[$0$][valid value of simple type] // `Unit`
Or[$\#$][valid or spoiled value of simple type] // `Unit`
Or[$bot$][spoiled value of simple type] // `Unit`
Or[$lambda type+ stmt$][function pointer value] // `Fun`
Or[$rf deepvalue$][reference value, contains label of the value in the memory] // `Ref`
Or[$[deepvalue+]$][tuple value] // `Prod`
Or[$rf deepValue$][reference value, contains label of the value in the memory] // `Ref`
Or[$[deepValue+]$][tuple value] // `Prod`
}
),
Prod(
@ -146,22 +164,23 @@
Or[$\#$][valid or spoiled value of simple type] // `Unit`
Or[$bot$][spoiled value of simple type] // `Unit`
Or[$lambda type+ stmt$][function pointer value] // `Fun`
Or[$rf LL$][reference value, contains label of the value in the memory] // `Ref`
// FIXME: embed mode into value for simplification ??
Or[$rf copyTag LL$][reference value, contains label of the value in the memory] // `Ref`
Or[$[value+]$][tuple value] // `Prod`
}
),
)
#deepvalue - полное значение, #value - слой значения, привязан к конкретной памяти $mu$
#deepValue - полное значение, #value - слой значения, привязан к конкретной памяти $mu$
Значения, могут лежать в переменных и передаваться как аргументы функций (то, во что вычисляется $expr$)
$v in value$ - произвольное значение
Получение #value по #deepvalue:
- $rf LL xarrowSquiggly(mu)_#[deep] rf mu[LL]$
Получение #deepValue по #value:
- $rf c l xarrowSquiggly(mu)_#[deep] rf c mu[l]$
- $* xarrowSquiggly(mu)_#[deep] *$
где $*$ - произвольный конструктор значения кроме $rf$
где $*$ - произвольный конструктор значения, кроме $rf$
== Memory Model
@ -173,17 +192,16 @@ $v in value$ - произвольное значение
- $LL$ - множество меток памяти
- $mem := LL -> value, space mu : mem$ - память, частично определённая функция
- $l in LL$ - новый тег памяти (ранее не использованный)
- `next` - получение следующей неиспользованной метки
- `next` - получение следующей неиспользованной метки в памяти
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add value to memory],
$l' = #[next] (l)$,
$l = #[next] (mu)$,
// TODO: check that access is what required ??
$cl mu, l cr xarrowSquiggly(v)_#[add] cl mu [l <- v], l' cr$,
$cl mu cr xarrowSquiggly(v)_#[add] cl l, mu [l <- v] cr$,
)
))
@ -260,7 +278,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access path],
name: [ tuple access path],
$x tpath p$,
@ -273,7 +291,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ variable typing],
name: [ variable type access],
$x : t_x ttype @x : t_x$,
)
@ -281,7 +299,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ reference typing],
name: [ reference type access],
$x tpath p$,
$x : t_x ttype p : rf mode t_p$,
@ -291,7 +309,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ tuple type access],
$x tpath p$,
$x : t_x ttype p : [t_1, ... t_n]$,
@ -300,34 +318,34 @@ $s in stmt, f in X, x in X, a in X$
))
]
- #[ Получение тега поля
- #[ Получение read-write тега поля
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ variable typing],
name: [ variable rw tag access],
$t_x = rf mode t$,
$x : t_x tmode @x -> mode$,
$t_x = r w ()$,
$x : t_x tmode @x -> cr r w cl$,
)
))
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ reference typing],
name: [ reference rw tag access],
$x tpath p$,
$x : t_x tmode p : rf mode t_p$,
$x : t_x tmode *p : t_p$,
$x : t_x tmode p -> cr r w cl$,
$x : t_x tmode *p -> cr r w cl$,
)
))
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ tuple rw tag access],
$x tpath p$,
$x : t_x tmode p : [t_1, ... t_n]$,
$x : t_x tmode p.i : t_i$,
$x : t_x tmode p -> cr r w cl$,
$x : t_x tmode p.i -> cr r w cl$,
)
))
]
@ -336,7 +354,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ variable typing],
name: [ variable value access],
$x eqmu v_x tval @x eqmu v_x$,
)
@ -344,7 +362,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ reference typing],
name: [ reference value access],
$x tpath p$,
$x eqmu v_x tval p eqmu rf l$,
@ -354,7 +372,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ tuple value access],
$x tpath p$,
$x eqmu v_x tmode p eqmu [v_1, ... v_n]$,
@ -367,11 +385,11 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ variable typing],
name: [ access],
$v_x = rf l$,
$x eqmu v_x tval p eqmu rf l$,
$x eqmu v_x tmode p arrmu l$,
)
))
@ -381,7 +399,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ access],
$x tpath p$,
$x : sigma[x].2 ttype p : t$,
@ -390,15 +408,15 @@ $s in stmt, f in X, x in X, a in X$
))
]
- #[ Получение тега поля по окружению
- #[ Получение read-write тега поля по окружению
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ access],
$x tpath p$,
$x : sigma[x].2 tmode p -> mode$,
$sigma temode p -> mode$,
$x : sigma[x].2 tmode p -> cr r space w cl$,
$sigma temode p -> cr r space w cl$,
)
))
]
@ -407,7 +425,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ access],
$x tpath p$,
$x eqmu sigma[x].1 tval p eqmu v$,
@ -420,7 +438,7 @@ $s in stmt, f in X, x in X, a in X$
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ access typing],
name: [ access],
$x tpath p$,
$x eqmu sigma[x].1 tlabel p arrmu l$,
@ -429,34 +447,37 @@ $s in stmt, f in X, x in X, a in X$
))
]
=== Mode Correctness
=== Mode Accessors
Функции проверки тегов, имеют тип $mode -> #[bool]$:
#let modevar = $(i space o)$
#let modevar = $(r space w space c space i space o)$
$ isIn modevar = i == In $
$ isOut modevar = o == Out $
$ isRead modevar = r == "Read" $
$ isAlwaysWrite modevar = w == square "Write" $
$ isPossibleWrite modevar = w == diamond "Write" || w == square "Write" $
$ isRef modevar = c == "Ref" $
$ isCopy modevar = c == "Copy" $
$ isIn modevar = i == "In" $
$ isOut modevar = o == "Out" $
// FIXME: move to new mode model
// === Mode Correctness
Требования к тегам:
// Функции проверки тегов, имеют тип $mode -> #[bool]$:
$ isOut mode -> isAlwaysWrite mode $
$ isRead mode -> isIn mode $
// #let modevar = $(r space w space c space i space o)$
// $ isRead modevar = r == "Read" $
// $ isAlwaysWrite modevar = w == square "Write" $
// $ isPossibleWrite modevar = w == diamond "Write" || w == square "Write" $
// $ isRef modevar = c == "Ref" $
// $ isCopy modevar = c == "Copy" $
// $ isIn modevar = i == "In" $
// $ isOut modevar = o == "Out" $
// Требования к тегам:
// $ isOut mode -> isAlwaysWrite mode $
// $ isRead mode -> isIn mode $
// TODO: rest conditions ??
=== Eval Rules
// FIXME: make connected to syntax
*TODO*
#h(10pt)
#let args = `args`
#[
@ -481,124 +502,170 @@ $ isRead mode -> isIn mode $
// TODO: introduce spep env argument ??
#h(10pt)
=== Moded Type Correctness
=== Correctness
#let tcorrect = $attach(tack.r, br: #[correct])$
// TODO: FIXME: well formatness for mode, extract
// TODO: FIXME: check for mode, is recursion required ??
// TODO: FIXME: check mode & access corectness in os correct
// TODO: check all requirements
$ sigma in env, space mu in mem, space m in mode,
space c in copyTag, space r, r' in readTag, space w, w' in writeTag,
space v in value, space t, t' in type $
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ is correct],
$isOut mode -> isAlwaysWrite mode$, // NOTE; strong requirment should write
$isRead mode -> isIn mode$,
$isPossibleWrite mode and (isOut mode or not isCopy mode) -> isAlwaysWrite pathenvmode(sigma, x)$, // NOTE: may mode => should sigma(x)
$isRead mode -> pathenvval(mu, sigma, x) != bot and pathenvval(mu, sigma, x) != X$,
name: [ unit assignment tags correctness],
$isCorrect_(cl sigma, mu cr) (mode, x)$,
$r = Read => isIn m$,
$isOut m => w = AlwaysWrite$,
// $sigma temode x -> cr r' space w' cl$, // NOTE: not required, value passed
$(w = AlwaysWrite or w = MaybeWrite) and (isOut m or c = Ref) => w' = AlwaysWrite$,
// $sigma, mu teval x eqmu v$, // NOTE: not required, value passed
$v in {0, \#, bot}$,
$r = Read => v = 0$,
$sigma, mu, m, c tcorrect v : r' space w' () -> r space w ()$,
)
))
#h(10pt)
=== Call Initialization
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ ref assignment tags correctness],
Отсутствующий нижний индекс ($ref$, $copy$) означает произвольный индекс.
Считается, что выбранный индекс одинаков в рамках одного правила.
$sigma, mu, m, c_r tcorrect v : t -> t'$,
// NOTE: no empty type
// #align(center, prooftree(
// vertical-spacing: 4pt,
// rule(
// name: [ add paths init],
// TODO: FIXME: which tag translations are correct ?? <- only assignee?
$sigma, mu, m, c tcorrect rf c_r space v : rf c' space t -> rf c_r space t'$,
)
))
// $cl sigma, mu, l cr stretch(~>)^nothing cl sigma, mu, l cr$,
// )
// ))
// #h(10pt)
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths field by copy],
name: [ tuple assignmenttags correctness],
$sigma, mu, m, c tcorrect v_1 : t_1 -> t'_1$,
$...$,
$sigma, mu, m, c tcorrect v_n : t_n -> t'_n$,
$sigma, mu, m, c tcorrect [v_1, ... v_n] : [t_1, ..., t_n] -> [t'_1, t'_n]$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ function pointer tags correctness],
$sigma, mu, m, c tcorrect lambda space overline(t) space s : lambda space overline(t) -> lambda space overline(t)$,
)
))
#h(10pt)
=== Value Construction
#let new = `new`
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ new $0$ value],
// TODO: check that access is what required ??
$cl sigma, mu, l cr xarrowSquiggly(p : ())_copy cl pathenvmem(sigma, p) <- l, mu [l <- 0], l + 1 cr$,
$cl 0, mu cr xarrowSquiggly(space)_new cl 0, mu cr$,
)
))
#h(10pt)
// NOTE: do nothing, ref init by default
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths field by reference],
$cl sigma, mu, l cr xarrowSquiggly(p : ())_ref cl sigma, mu, l cr$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths ref],
$cl sigma, mu, l cr xarrowSquiggly(*p : t)_ref cl sigma', mu', l' cr$,
$isRef mode$,
name: [ new $\#$ value],
$cl sigma, mu, l cr xarrowSquiggly(p : \& mode t) cl sigma', mu', l' cr$,
// TODO: check that access is what required ??
$cl \#, mu cr xarrowSquiggly(space)_new cl \#, mu cr$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths ref],
$cl sigma, mu, l cr xarrowSquiggly(*p : t)_copy cl sigma, mu, l cr$,
$isCopy mode$,
name: [ new $bot$ value],
$cl sigma, mu, l cr xarrowSquiggly(p : \& mode t) cl sigma', mu', l' cr$,
$cl bot, mu cr xarrowSquiggly(space)_new cl bot, mu cr$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths tuple],
$cl sigma, mu, l cr xarrowSquiggly(p.1 : t_1) cl sigma_1, mu_1, l_1 cr$,
name: [ new funciton pointer value],
$cl lambda overline(t) s, mu cr xarrowSquiggly(space)_new cl lambda overline(t) s, mu cr$,
)
))
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ new reference ref value],
$cl rf Ref l, mu cr xarrowSquiggly(space)_new cl rf Ref l, mu cr$,
)
))
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ new reference copy value],
$cl mu[l], mu cr xarrowSquiggly(space)_new cl v, mu_v cr$,
$cl mu_v cr xarrowSquiggly(v)_#[add] cl l', mu_a cr$,
$cl rf Copy l, mu cr xarrowSquiggly(space)_new cl rf Copy l', mu_a cr$,
)
))
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ new tuple value],
$cl v_1, mu_0 cr xarrowSquiggly(space)_new cl lambda v'_1, mu_1 cr$,
$...$,
$cl sigma_(n - 1), mu_(n - 1), l_(n - 1) cr xarrowSquiggly(p.n : t_n) cl sigma_n, mu_n, l_n cr$,
$cl v_n, mu_(n - 1) cr xarrowSquiggly(space)_new cl lambda v'_n, mu_n cr$,
$cl sigma, mu, l cr xarrowSquiggly(p : [t_1, ... t_n]) cl sigma_n, mu_n, l_n cr$,
$cl [v_1, ... v_n], mu_0 cr xarrowSquiggly(space)_new cl [v'_1, ... v'_n], mu_n cr$,
)
))
#h(10pt)
=== Value Update
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ add paths funciton pointer],
#let write = `write`
$cl sigma, mu, l cr xarrowSquiggly(F_x) cl sigma, mu, l cr$,
)
))
#h(10pt)
*TODO: write to value*
=== Call Finalization
// FIXME: make connected to syntax
*TODO*
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
@ -670,6 +737,9 @@ $ isRead mode -> isIn mode $
=== Function Evaluation
// FIXME: make connected to syntax
*TODO*
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
@ -719,22 +789,22 @@ $ isRead mode -> isIn mode $
=== Statement Evaluation
// FIXME: make connected to syntax
*TODO: check type of lambda?, args from type?*
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ CALL $f space overline(x)$],
name: [ CALL $f space overline(p)$],
$cl [], mu, l cr
xarrowDashed(d space @ space overline(x))
xarrowDashed(f space @ space overline(p))
cl sigma', mu', l' cr$,
// TODO: FIXME define args in some way
$mu attach(stretch(=>)^args_sigma, tr: *) gamma$,
$DD(f) := d$,
$cl sigma, mu, l cr
xarrow("CALL" f space overline(x))
xarrow("CALL" f space overline(p))
cl sigma, gamma, l cr$,
)
))
@ -744,32 +814,12 @@ $ isRead mode -> isIn mode $
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ CALL_LAM $y space overline(x)$],
name: [ READ $p$],
$pathenvtype(sigma, y) = F_f$,
$mu, sigma teval p eqmu 0$,
$cl sigma, mu, l cr
xarrow("CALL" f space overline(x))
cl sigma, gamma, l cr$,
$cl sigma, mu, l cr
xarrow("CALL_LAM" y space overline(x))
cl sigma, gamma, l cr$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ READ $x$],
$pathenvval(mu, sigma, x) != bot$,
$pathenvval(mu, sigma, x) != X$,
$cl sigma, mu, l cr
xarrow("READ" x)
xarrow("READ" p)
cl sigma, mu, l cr$,
)
))
@ -781,11 +831,38 @@ $ isRead mode -> isIn mode $
rule(
name: [ WRITE $x$],
$isPossibleWrite sigma(x)$,
$sigma temode p -> cr r space w cl$,
$cl sigma, mu, l cr
xarrow("WRITE" x)
cl sigma, pathenvval(mu, sigma, x) <- 0, l cr$,
$w == MaybeWrite or w == AlwaysWrite$,
$x tpath p$,
$mu[x] xarrowSquiggly(p)_write v$,
$cl sigma, mu cr
xarrow("WRITE" p)
cl sigma, mu[x <- v] cr$,
)
))
#h(10pt)
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ $s \; t$],
$cl sigma, mu cr
stretch(->)^s
cl sigma_s, mu_s cr$,
$cl sigma, mu cr
stretch(->)^t
cl sigma_t, mu_t cr$,
$cl sigma, mu, cr
xarrow(s \; t)
cl sigma_t, mu_t cr$,
)
))
@ -793,26 +870,27 @@ $ isRead mode -> isIn mode $
#let combine = `combine`
*TODO: combine replacement* // FIXME
#align(center, prooftree(
vertical-spacing: 4pt,
rule(
name: [ CHOICE $overline(s)$ $overline(t)$],
name: [ $s | t$],
$cl sigma, mu, l cr
attach(stretch(->)^overline(s), tr: *)
stretch(->)^s
cl sigma_s, mu_s, l_s cr$,
$cl sigma, mu, l cr
attach(stretch(->)^overline(t), tr: *)
stretch(->)^t
cl sigma_t, mu_t, l_t cr$,
$l_t = l_s$,
$sigma_s = sigma_t$,
$mu' = combine(mu_s, mu_t)$,
// TODO changes ?? two ways ??
$cl sigma, mu, l cr
xarrow("CHOICE" overline(s) space overline(t))
cl sigma, combine(mu_s, mu_t), l cr$,
$cl sigma, mu cr
xarrow(s | t)
cl sigma_t, mu' cr$,
)
))
@ -820,9 +898,16 @@ $ isRead mode -> isIn mode $
=== Combination
*TODO: rewrite as rules, fix* // FIXME
$ combine(mu_1, mu_2)[i] = combine_e (mu_1[i], mu_2[i]) $
$ combine_e (bot, bot) = bot $
$ combine_e (0, 0) = 0 $
$ combine_e (\_, \_) = X $
$ combine_e (\_, \_) = \# $
// FIXME: ref to combined memory
$ combine_e (rf c l_1, rf c' l_2) | c == c' = rf c combine_e(mu_1[l_1], mu_2[l_2])$
$ combine_e (v^1_1, ... v^1_n, v^2_1 ... v^2_n) = [combine_e(v^1_1, v^2_1), ..., combine_e(v^1_n, v^2_n)]$
$ combine_e (lambda space overline(t_1) space s_1, lambda space overline(t_2) space s_2) | overline(t_1) == overline(t_2) = lambda space overline(t_1) space s_1 $
// TODO: FIXME: statemient in lambda is not important ??
]