Nuprl Lemma : member-fset-pair
∀[T:Type]. ∀eq:EqDecider(T). ∀x,y,z:T.  uiff(z ∈ {x,y};(z = x ∈ T) ∨ (z = y ∈ T))
Proof
Definitions occuring in Statement : 
fset-pair: {a,b}, 
fset-member: a ∈ s, 
deq: EqDecider(T), 
uiff: uiff(P;Q), 
uall: ∀[x:A]. B[x], 
all: ∀x:A. B[x], 
or: P ∨ Q, 
universe: Type, 
equal: s = t ∈ T
Definitions unfolded in proof : 
uall: ∀[x:A]. B[x], 
all: ∀x:A. B[x], 
member: t ∈ T, 
implies: P ⇒ Q, 
guard: {T}, 
fset-pair: {a,b}, 
fset-member: a ∈ s, 
top: Top, 
uiff: uiff(P;Q), 
and: P ∧ Q, 
uimplies: b supposing a, 
prop: ℙ, 
or: P ∨ Q, 
iff: P ⇐⇒ Q, 
assert: ↑b, 
ifthenelse: if b then t else f fi , 
bfalse: ff, 
rev_implies: P ⇐ Q, 
eqof: eqof(d), 
decidable: Dec(P), 
not: ¬A, 
false: False
Lemmas referenced : 
deq-implies, 
deq_member_cons_lemma, 
deq_member_nil_lemma, 
deq_wf, 
or_wf, 
equal_wf, 
bor_wf, 
eqof_wf, 
bfalse_wf, 
assert_wf, 
false_wf, 
uiff_wf, 
assert_witness, 
iff_transitivity, 
iff_weakening_uiff, 
assert_of_bor, 
safe-assert-deq
Rules used in proof : 
sqequalSubstitution, 
sqequalTransitivity, 
computationStep, 
sqequalReflexivity, 
isect_memberFormation, 
lambdaFormation, 
cut, 
introduction, 
extract_by_obid, 
sqequalHypSubstitution, 
isectElimination, 
thin, 
because_Cache, 
independent_functionElimination, 
hypothesis, 
sqequalRule, 
dependent_functionElimination, 
isect_memberEquality, 
voidElimination, 
voidEquality, 
hypothesisEquality, 
cumulativity, 
universeEquality, 
independent_pairFormation, 
applyEquality, 
addLevel, 
productElimination, 
rename, 
independent_isectElimination, 
orFunctionality, 
unionElimination, 
inlFormation, 
inrFormation, 
equalitySymmetry
Latex:
\mforall{}[T:Type].  \mforall{}eq:EqDecider(T).  \mforall{}x,y,z:T.    uiff(z  \mmember{}  \{x,y\};(z  =  x)  \mvee{}  (z  =  y))
Date html generated:
2017_04_17-AM-09_18_59
Last ObjectModification:
2017_02_27-PM-05_22_29
Theory : finite!sets
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