Nuprl Lemma : strat2play-invariant-1
∀g:SimpleGame. ∀n:ℕ. ∀s:win2strat(g;n). ∀moves:strat2play(g;n;s).
  ((moves[0] = InitialPos(g) ∈ Pos(g))
  ∧ (∀i:ℕn + 1
       ((↓Legal1(moves[2 * i];moves[(2 * i) + 1]))
       ∧ (i < n
         ⇒ ((↓Legal2(moves[(2 * i) + 1];moves[2 * (i + 1)]))
            ∧ (moves[2 * (i + 1)] = (s play-truncate(moves;2 * (i + 1))) ∈ Pos(g)))))))
Proof
Definitions occuring in Statement : 
strat2play: strat2play(g;n;s), 
win2strat: win2strat(g;n), 
play-truncate: play-truncate(f;m), 
play-item: moves[i], 
sg-legal2: Legal2(x;y), 
sg-legal1: Legal1(x;y), 
sg-init: InitialPos(g), 
sg-pos: Pos(g), 
simple-game: SimpleGame, 
seq-item: s[i], 
int_seg: {i..j-}, 
nat: ℕ, 
less_than: a < b, 
all: ∀x:A. B[x], 
squash: ↓T, 
implies: P ⇒ Q, 
and: P ∧ Q, 
apply: f a, 
multiply: n * m, 
add: n + m, 
natural_number: $n, 
equal: s = t ∈ T
Definitions unfolded in proof : 
all: ∀x:A. B[x], 
uall: ∀[x:A]. B[x], 
member: t ∈ T, 
nat: ℕ, 
implies: P ⇒ Q, 
false: False, 
ge: i ≥ j , 
guard: {T}, 
uimplies: b supposing a, 
prop: ℙ, 
and: P ∧ Q, 
squash: ↓T, 
int_seg: {i..j-}, 
le: A ≤ B, 
less_than': less_than'(a;b), 
not: ¬A, 
decidable: Dec(P), 
or: P ∨ Q, 
iff: P ⇐⇒ Q, 
rev_implies: P ⇐ Q, 
uiff: uiff(P;Q), 
subtract: n - m, 
subtype_rel: A ⊆r B, 
top: Top, 
true: True, 
strat2play: strat2play(g;n;s), 
eq_int: (i =z j), 
ifthenelse: if b then t else f fi , 
btrue: tt, 
cand: A c∧ B, 
sq_type: SQType(T), 
lelt: i ≤ j < k, 
win2strat: win2strat(g;n), 
bfalse: ff, 
so_lambda: λ2x.t[x], 
so_apply: x[s], 
play-len: ||moves||, 
play-truncate: play-truncate(f;m), 
play-item: moves[i]
Lemmas referenced : 
nat_properties, 
less_than_transitivity1, 
less_than_irreflexivity, 
ge_wf, 
less_than_wf, 
int_seg_wf, 
strat2play_wf, 
win2strat_wf, 
false_wf, 
le_wf, 
decidable__le, 
subtract_wf, 
not-ge-2, 
less-iff-le, 
condition-implies-le, 
minus-one-mul, 
zero-add, 
minus-one-mul-top, 
minus-add, 
minus-minus, 
add-associates, 
add-swap, 
add-commutes, 
add_functionality_wrt_le, 
add-zero, 
le-add-cancel, 
le_weakening2, 
nat_wf, 
simple-game_wf, 
decidable__int_equal, 
subtype_base_sq, 
int_subtype_base, 
int_seg_properties, 
int_seg_subtype, 
int_seg_cases, 
eq_int_wf, 
le_weakening, 
assert_wf, 
bnot_wf, 
not_wf, 
equal-wf-base, 
bool_cases, 
bool_wf, 
bool_subtype_base, 
eqtt_to_assert, 
assert_of_eq_int, 
eqff_to_assert, 
iff_transitivity, 
iff_weakening_uiff, 
assert_of_bnot, 
add-is-int-iff, 
decidable__lt, 
not-lt-2, 
le-add-cancel-alt, 
lelt_wf, 
set_subtype_base, 
not-equal-2, 
minus-zero, 
subtract-add-cancel, 
mul-distributes, 
mul-commutes, 
not-le-2, 
le-add-cancel2, 
mul_preserves_le, 
play-item_wf, 
mul-associates, 
mul-distributes-right, 
zero-mul, 
squash_wf, 
true_wf, 
sg-legal2_wf, 
sg-pos_wf, 
subtype_rel_self, 
iff_weakening_equal, 
play-truncate_wf, 
equal-wf-T-base, 
play-len_wf, 
equal_wf, 
set_wf, 
seq-truncate-item, 
seq-item_wf, 
seq-len_wf
Rules used in proof : 
sqequalSubstitution, 
sqequalTransitivity, 
computationStep, 
sqequalReflexivity, 
lambdaFormation, 
cut, 
introduction, 
extract_by_obid, 
sqequalHypSubstitution, 
isectElimination, 
thin, 
hypothesisEquality, 
hypothesis, 
setElimination, 
rename, 
intWeakElimination, 
natural_numberEquality, 
independent_isectElimination, 
independent_functionElimination, 
voidElimination, 
sqequalRule, 
lambdaEquality, 
dependent_functionElimination, 
productElimination, 
independent_pairEquality, 
axiomEquality, 
imageElimination, 
imageMemberEquality, 
baseClosed, 
addEquality, 
because_Cache, 
dependent_set_memberEquality, 
independent_pairFormation, 
unionElimination, 
applyEquality, 
isect_memberEquality, 
voidEquality, 
intEquality, 
minusEquality, 
instantiate, 
cumulativity, 
equalityTransitivity, 
equalitySymmetry, 
hypothesis_subsumption, 
dependentIntersectionElimination, 
applyLambdaEquality, 
promote_hyp, 
impliesFunctionality, 
baseApply, 
closedConclusion, 
multiplyEquality, 
universeEquality, 
functionEquality, 
setEquality, 
addLevel, 
hyp_replacement, 
levelHypothesis
Latex:
\mforall{}g:SimpleGame.  \mforall{}n:\mBbbN{}.  \mforall{}s:win2strat(g;n).  \mforall{}moves:strat2play(g;n;s).
    ((moves[0]  =  InitialPos(g))
    \mwedge{}  (\mforall{}i:\mBbbN{}n  +  1
              ((\mdownarrow{}Legal1(moves[2  *  i];moves[(2  *  i)  +  1]))
              \mwedge{}  (i  <  n
                  {}\mRightarrow{}  ((\mdownarrow{}Legal2(moves[(2  *  i)  +  1];moves[2  *  (i  +  1)]))
                        \mwedge{}  (moves[2  *  (i  +  1)]  =  (s  play-truncate(moves;2  *  (i  +  1)))))))))
 Date html generated: 
2018_07_25-PM-01_32_57
 Last ObjectModification: 
2018_06_12-PM-00_30_13
Theory : co-recursion
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