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Theorem List for Metamath Proof Explorer - 15901-16000   *Has distinct variable group(s)
TypeLabelDescription
Statement

Syntaxcnx 15901 Extend class notation with the structure component index extractor.
class ndx

Syntaxcsts 15902 Set components of a structure.
class sSet

Syntaxcslot 15903 Extend class notation with the slot function.
class Slot 𝐴

Syntaxcbs 15904 Extend class notation with the class of all base set extractors.
class Base

Syntaxcress 15905 Extend class notation with the extensible structure builder restriction operator.
class s

Definitiondf-struct 15906* Define a structure with components in 𝑀...𝑁. This is not a requirement for groups, posets, etc., but it is a useful assumption for component extraction theorems.

As mentioned in the section header, an "extensible structure should be implemented as a function (a set of ordered pairs)". The current definition, however, is less restrictive: it allows for classes which contain the empty set to be extensible structures. Because of 0nelfun 5944, such classes cannot be functions. Without the empty set, however, a structure must be a function, see structn0fun 15916: 𝐹 Struct 𝑋 → Fun (𝐹 ∖ {∅}).

Allowing an extensible structure to contain the empty set ensures that expressions like {⟨𝐴, 𝐵⟩, ⟨𝐶, 𝐷⟩} are structures without asserting or implying that 𝐴, 𝐵, 𝐶 and 𝐷 are sets (if 𝐴 or 𝐵 is a proper class, then 𝐴, 𝐵⟩ = ∅, see opprc 4456). This is used critically in strle1 16020, strle2 16021, strle3 16022 and strleun 16019 to avoid sethood hypotheses on the "payload" sets: without this, ipsstr 16071 and theorems like it will have many sethood assumptions, and may not even be usable in the empty context. Instead, the sethood assumption is deferred until it is actually needed, e.g. ipsbase 16072, which requires that the base set is a set but not any of the other components. Usually, a concrete structure like fld does not contain the empty set, and therefore is a function, see cnfldfun 19806. (Contributed by Mario Carneiro, 29-Aug-2015.)

Struct = {⟨𝑓, 𝑥⟩ ∣ (𝑥 ∈ ( ≤ ∩ (ℕ × ℕ)) ∧ Fun (𝑓 ∖ {∅}) ∧ dom 𝑓 ⊆ (...‘𝑥))}

Definitiondf-ndx 15907 Define the structure component index extractor. See theorem ndxarg 15929 to understand its purpose. The restriction to ensures that ndx is a set. The restriction to some set is necessary since I is a proper class. In principle, we could have chosen or (if we revise all structure component definitions such as df-base 15910) another set such as the set of finite ordinals ω (df-om 7108). (Contributed by NM, 4-Sep-2011.)
ndx = ( I ↾ ℕ)

Definitiondf-slot 15908* Define the slot extractor for extensible structures. The class Slot 𝐴 is a function whose argument can be any set, although it is meaningful only if that set is a member of an extensible structure (such as a partially ordered set (df-poset 16993) or a group (df-grp 17472)).

Note that Slot 𝐴 is implemented as "evaluation at 𝐴". That is, (Slot 𝐴𝑆) is defined to be (𝑆𝐴), where 𝐴 will typically be a small nonzero natural number. Each extensible structure 𝑆 is a function defined on specific natural number "slots", and this function extracts the value at a particular slot.

The special "structure" ndx, defined as the identity function restricted to , can be used to extract the number 𝐴 from a slot, since (Slot 𝐴‘ndx) = 𝐴 (see ndxarg 15929). This is typically used to refer to the number of a slot when defining structures without having to expose the detail of what that number is (for instance, we use the expression (Base‘ndx) in theorems and proofs instead of its value 1).

The class Slot cannot be defined as (𝑥 ∈ V ↦ (𝑓 ∈ V ↦ (𝑓𝑥))) because each Slot 𝐴 is a function on the proper class V so is itself a proper class, and the values of functions are sets (fvex 6239). It is necessary to allow proper classes as values of Slot 𝐴 since for instance the class of all (base sets of) groups is proper. (Contributed by Mario Carneiro, 22-Sep-2015.)

Slot 𝐴 = (𝑥 ∈ V ↦ (𝑥𝐴))

Theoremsloteq 15909 Equality theorem for the Slot construction. (Contributed by BJ, 27-Dec-2021.)
(𝐴 = 𝐵 → Slot 𝐴 = Slot 𝐵)

Definitiondf-base 15910 Define the base set (also called underlying set or carrier set) extractor for extensible structures. (Contributed by NM, 4-Sep-2011.) (Revised by Mario Carneiro, 14-Aug-2015.)
Base = Slot 1

Definitiondf-sets 15911* Set a component of an extensible structure. This function is useful for taking an existing structure and "overriding" one of its components. For example, df-ress 15912 adjusts the base set to match its second argument, which has the effect of making subgroups, subspaces, subrings etc. from the original structures. Or df-mgp 18536, which takes a ring and overrides its addition operation with the multiplicative operation, so that we can consider the "multiplicative group" using group and monoid theorems, which expect the operation to be in the +g slot instead of the .r slot. (Contributed by Mario Carneiro, 1-Dec-2014.)
sSet = (𝑠 ∈ V, 𝑒 ∈ V ↦ ((𝑠 ↾ (V ∖ dom {𝑒})) ∪ {𝑒}))

Definitiondf-ress 15912* Define a multifunction restriction operator for extensible structures, which can be used to turn statements about rings into statements about subrings, modules into submodules, etc. This definition knows nothing about individual structures and merely truncates the Base set while leaving operators alone; individual kinds of structures will need to handle this behavior, by ignoring operators' values outside the range (like Ring), defining a function using the base set and applying that (like TopGrp), or explicitly truncating the slot before use (like MetSp).

(Credit for this operator goes to Mario Carneiro.)

See ressbas 15977 for the altered base set, and resslem 15980 (subrg0 18835, ressplusg 16040, subrg1 18838, ressmulr 16053) for the (un)altered other operations. (Contributed by Stefan O'Rear, 29-Nov-2014.)

s = (𝑤 ∈ V, 𝑥 ∈ V ↦ if((Base‘𝑤) ⊆ 𝑥, 𝑤, (𝑤 sSet ⟨(Base‘ndx), (𝑥 ∩ (Base‘𝑤))⟩)))

Theorembrstruct 15913 The structure relation is a relation. (Contributed by Mario Carneiro, 29-Aug-2015.)
Rel Struct

Theoremisstruct2 15914 The property of being a structure with components in (1st𝑋)...(2nd𝑋). (Contributed by Mario Carneiro, 29-Aug-2015.)
(𝐹 Struct 𝑋 ↔ (𝑋 ∈ ( ≤ ∩ (ℕ × ℕ)) ∧ Fun (𝐹 ∖ {∅}) ∧ dom 𝐹 ⊆ (...‘𝑋)))

Theoremstructex 15915 A structure is a set. (Contributed by AV, 10-Nov-2021.)
(𝐺 Struct 𝑋𝐺 ∈ V)

Theoremstructn0fun 15916 A structure witout the empty set is a function. (Contributed by AV, 13-Nov-2021.)
(𝐹 Struct 𝑋 → Fun (𝐹 ∖ {∅}))

Theoremisstruct 15917 The property of being a structure with components in 𝑀...𝑁. (Contributed by Mario Carneiro, 29-Aug-2015.)
(𝐹 Struct ⟨𝑀, 𝑁⟩ ↔ ((𝑀 ∈ ℕ ∧ 𝑁 ∈ ℕ ∧ 𝑀𝑁) ∧ Fun (𝐹 ∖ {∅}) ∧ dom 𝐹 ⊆ (𝑀...𝑁)))

Theoremstructcnvcnv 15918 Two ways to express the relational part of a structure. (Contributed by Mario Carneiro, 29-Aug-2015.)
(𝐹 Struct 𝑋𝐹 = (𝐹 ∖ {∅}))

Theoremstructfung 15919 The converse of the converse of a structure is a function. Closed form of structfun 15920. (Contributed by AV, 12-Nov-2021.)
(𝐹 Struct 𝑋 → Fun 𝐹)

Theoremstructfun 15920 Convert between two kinds of structure closure. (Contributed by Mario Carneiro, 29-Aug-2015.) (Proof shortened by AV, 12-Nov-2021.)
𝐹 Struct 𝑋       Fun 𝐹

Theoremstructfn 15921 Convert between two kinds of structure closure. (Contributed by Mario Carneiro, 29-Aug-2015.)
𝐹 Struct ⟨𝑀, 𝑁       (Fun 𝐹 ∧ dom 𝐹 ⊆ (1...𝑁))

Theoremslotfn 15922 A slot is a function on sets, treated as structures. (Contributed by Mario Carneiro, 22-Sep-2015.)
𝐸 = Slot 𝑁       𝐸 Fn V

Theoremstrfvnd 15923 Deduction version of strfvn 15926. (Contributed by Mario Carneiro, 15-Nov-2014.)
𝐸 = Slot 𝑁    &   (𝜑𝑆𝑉)       (𝜑 → (𝐸𝑆) = (𝑆𝑁))

Theorembasfn 15924 The base set extractor is a function on V. (Contributed by Stefan O'Rear, 8-Jul-2015.)
Base Fn V

Theoremwunndx 15925 Closure of the index extractor in an infinite weak universe. (Contributed by Mario Carneiro, 12-Jan-2017.)
(𝜑𝑈 ∈ WUni)    &   (𝜑 → ω ∈ 𝑈)       (𝜑 → ndx ∈ 𝑈)

Theoremstrfvn 15926 Value of a structure component extractor 𝐸. Normally, 𝐸 is a defined constant symbol such as Base (df-base 15910) and 𝑁 is a fixed integer such as 1. 𝑆 is a structure, i.e. a specific member of a class of structures such as Poset (df-poset 16993) where 𝑆 ∈ Poset.

Note: Normally, this theorem shouldn't be used outside of this section, because it requires hard-coded index values. Instead, use strfv 15954. (Contributed by NM, 9-Sep-2011.) (Revised by Mario Carneiro, 6-Oct-2013.) (New usage is discouraged.)

𝑆 ∈ V    &   𝐸 = Slot 𝑁       (𝐸𝑆) = (𝑆𝑁)

Theoremstrfvss 15927 A structure component extractor produces a value which is contained in a set dependent on 𝑆, but not 𝐸. This is sometimes useful for showing sethood. (Contributed by Mario Carneiro, 15-Aug-2015.)
𝐸 = Slot 𝑁       (𝐸𝑆) ⊆ ran 𝑆

Theoremwunstr 15928 Closure of a structure index in a weak universe. (Contributed by Mario Carneiro, 12-Jan-2017.)
𝐸 = Slot 𝑁    &   (𝜑𝑈 ∈ WUni)    &   (𝜑𝑆𝑈)       (𝜑 → (𝐸𝑆) ∈ 𝑈)

Theoremndxarg 15929 Get the numeric argument from a defined structure component extractor such as df-base 15910. (Contributed by Mario Carneiro, 6-Oct-2013.)
𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ       (𝐸‘ndx) = 𝑁

Theoremndxid 15930 A structure component extractor is defined by its own index. This theorem, together with strfv 15954 below, is useful for avoiding direct reference to the hard-coded numeric index in component extractor definitions, such as the 1 in df-base 15910 and the 10 in df-ple 16008, making it easier to change should the need arise.

For example, we can refer to a specific poset with base set 𝐵 and order relation 𝐿 using {⟨(Base‘ndx), 𝐵⟩, ⟨(le‘ndx), 𝐿⟩} rather than {⟨1, 𝐵⟩, 10, 𝐿⟩}. The latter, while shorter to state, requires revision if we later change 10 to some other number, and it may also be harder to remember. (Contributed by NM, 19-Oct-2012.) (Revised by Mario Carneiro, 6-Oct-2013.) (Proof shortened by BJ, 27-Dec-2021.)

𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ       𝐸 = Slot (𝐸‘ndx)

TheoremndxidOLD 15931 Obsolete proof of ndxid 15930 as of 28-Dec-2021. (Contributed by NM, 19-Oct-2012.) (Revised by Mario Carneiro, 6-Oct-2013.) (Proof modification is discouraged.) (New usage is discouraged.)
𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ       𝐸 = Slot (𝐸‘ndx)

Theoremstrndxid 15932 The value of a structure component extractor is the value of the corresponding slot of the structure. (Contributed by AV, 13-Mar-2020.)
(𝜑𝑆𝑉)    &   𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ       (𝜑 → (𝑆‘(𝐸‘ndx)) = (𝐸𝑆))

Theoremreldmsets 15933 The structure override operator is a proper operator. (Contributed by Stefan O'Rear, 29-Jan-2015.)
Rel dom sSet

Theoremsetsvalg 15934 Value of the structure replacement function. (Contributed by Mario Carneiro, 30-Apr-2015.)
((𝑆𝑉𝐴𝑊) → (𝑆 sSet 𝐴) = ((𝑆 ↾ (V ∖ dom {𝐴})) ∪ {𝐴}))

Theoremsetsval 15935 Value of the structure replacement function. (Contributed by Mario Carneiro, 1-Dec-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
((𝑆𝑉𝐵𝑊) → (𝑆 sSet ⟨𝐴, 𝐵⟩) = ((𝑆 ↾ (V ∖ {𝐴})) ∪ {⟨𝐴, 𝐵⟩}))

Theoremsetsidvald 15936 Value of the structure replacement function, deduction version. (Contributed by AV, 14-Mar-2020.)
𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ    &   (𝜑𝑆𝑉)    &   (𝜑 → Fun 𝑆)    &   (𝜑 → (𝐸‘ndx) ∈ dom 𝑆)       (𝜑𝑆 = (𝑆 sSet ⟨(𝐸‘ndx), (𝐸𝑆)⟩))

Theoremfvsetsid 15937 The value of the structure replacement function for its first argument is its second argument. (Contributed by SO, 12-Jul-2018.)
((𝐹𝑉𝑋𝑊𝑌𝑈) → ((𝐹 sSet ⟨𝑋, 𝑌⟩)‘𝑋) = 𝑌)

Theoremfsets 15938 The structure replacement function is a function. (Contributed by SO, 12-Jul-2018.)
(((𝐹𝑉𝐹:𝐴𝐵) ∧ 𝑋𝐴𝑌𝐵) → (𝐹 sSet ⟨𝑋, 𝑌⟩):𝐴𝐵)

Theoremsetsdm 15939 The domain of a structure with replacement is the domain of the original structure extended by the index of the replacement. (Contributed by AV, 7-Jun-2021.)
((𝐺𝑉𝐸𝑊) → dom (𝐺 sSet ⟨𝐼, 𝐸⟩) = (dom 𝐺 ∪ {𝐼}))

Theoremsetsfun 15940 A structure with replacement is a function if the original structure is a function. (Contributed by AV, 7-Jun-2021.)
(((𝐺𝑉 ∧ Fun 𝐺) ∧ (𝐼𝑈𝐸𝑊)) → Fun (𝐺 sSet ⟨𝐼, 𝐸⟩))

Theoremsetsfun0 15941 A structure with replacement without the empty set is a function if the original structure without the empty set is a function. This variant of setsfun 15940 is useful for proofs based on isstruct2 15914 which requires Fun (𝐹 ∖ {∅}) for 𝐹 to be an extensible structure. (Contributed by AV, 7-Jun-2021.)
(((𝐺𝑉 ∧ Fun (𝐺 ∖ {∅})) ∧ (𝐼𝑈𝐸𝑊)) → Fun ((𝐺 sSet ⟨𝐼, 𝐸⟩) ∖ {∅}))

Theoremsetsn0fun 15942 The value of the structure replacement function (without the empty set) is a function if the structure (without the empty set)is a function. (Contributed by AV, 7-Jun-2021.) (Revised by AV, 16-Nov-2021.)
(𝜑𝑆 Struct 𝑋)    &   (𝜑𝐼𝑈)    &   (𝜑𝐸𝑊)       (𝜑 → Fun ((𝑆 sSet ⟨𝐼, 𝐸⟩) ∖ {∅}))

Theoremsetsstruct2 15943 An extensible structure with a replaced slot is an extensible structure. (Contributed by AV, 14-Nov-2021.)
(((𝐺 Struct 𝑋𝐸𝑉𝐼 ∈ ℕ) ∧ 𝑌 = ⟨if(𝐼 ≤ (1st𝑋), 𝐼, (1st𝑋)), if(𝐼 ≤ (2nd𝑋), (2nd𝑋), 𝐼)⟩) → (𝐺 sSet ⟨𝐼, 𝐸⟩) Struct 𝑌)

Theoremsetsexstruct2 15944* An extensible structure with a replaced slot is an extensible structure. (Contributed by AV, 14-Nov-2021.)
((𝐺 Struct 𝑋𝐸𝑉𝐼 ∈ ℕ) → ∃𝑦(𝐺 sSet ⟨𝐼, 𝐸⟩) Struct 𝑦)

Theoremsetsstruct 15945 An extensible structure with a replaced slot is an extensible structure. (Contributed by AV, 9-Jun-2021.) (Revised by AV, 14-Nov-2021.)
((𝐸𝑉𝐼 ∈ (ℤ𝑀) ∧ 𝐺 Struct ⟨𝑀, 𝑁⟩) → (𝐺 sSet ⟨𝐼, 𝐸⟩) Struct ⟨𝑀, if(𝐼𝑁, 𝑁, 𝐼)⟩)

TheoremsetsstructOLD 15946 Obsolete version of setsstruct 15945 as of 14-Nov-2021. (Contributed by AV, 9-Jun-2021.) (New usage is discouraged.) (Proof modification is discouraged.)
((𝐺𝑈𝐸𝑉𝐼 ∈ (ℤ𝑀)) → (𝐺 Struct ⟨𝑀, 𝑁⟩ → (𝐺 sSet ⟨𝐼, 𝐸⟩) Struct ⟨𝑀, if(𝐼𝑁, 𝑁, 𝐼)⟩))

Theoremwunsets 15947 Closure of structure replacement in a weak universe. (Contributed by Mario Carneiro, 12-Jan-2017.)
(𝜑𝑈 ∈ WUni)    &   (𝜑𝑆𝑈)    &   (𝜑𝐴𝑈)       (𝜑 → (𝑆 sSet 𝐴) ∈ 𝑈)

Theoremsetsres 15948 The structure replacement function does not affect the value of 𝑆 away from 𝐴. (Contributed by Mario Carneiro, 1-Dec-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
(𝑆𝑉 → ((𝑆 sSet ⟨𝐴, 𝐵⟩) ↾ (V ∖ {𝐴})) = (𝑆 ↾ (V ∖ {𝐴})))

Theoremsetsabs 15949 Replacing the same components twice yields the same as the second setting only. (Contributed by Mario Carneiro, 2-Dec-2014.)
((𝑆𝑉𝐶𝑊) → ((𝑆 sSet ⟨𝐴, 𝐵⟩) sSet ⟨𝐴, 𝐶⟩) = (𝑆 sSet ⟨𝐴, 𝐶⟩))

Theoremsetscom 15950 Component-setting is commutative when the x-values are different. (Contributed by Mario Carneiro, 5-Dec-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
𝐴 ∈ V    &   𝐵 ∈ V       (((𝑆𝑉𝐴𝐵) ∧ (𝐶𝑊𝐷𝑋)) → ((𝑆 sSet ⟨𝐴, 𝐶⟩) sSet ⟨𝐵, 𝐷⟩) = ((𝑆 sSet ⟨𝐵, 𝐷⟩) sSet ⟨𝐴, 𝐶⟩))

Theoremstrfvd 15951 Deduction version of strfv 15954. (Contributed by Mario Carneiro, 15-Nov-2014.)
𝐸 = Slot (𝐸‘ndx)    &   (𝜑𝑆𝑉)    &   (𝜑 → Fun 𝑆)    &   (𝜑 → ⟨(𝐸‘ndx), 𝐶⟩ ∈ 𝑆)       (𝜑𝐶 = (𝐸𝑆))

Theoremstrfv2d 15952 Deduction version of strfv 15954. (Contributed by Mario Carneiro, 30-Apr-2015.)
𝐸 = Slot (𝐸‘ndx)    &   (𝜑𝑆𝑉)    &   (𝜑 → Fun 𝑆)    &   (𝜑 → ⟨(𝐸‘ndx), 𝐶⟩ ∈ 𝑆)    &   (𝜑𝐶𝑊)       (𝜑𝐶 = (𝐸𝑆))

Theoremstrfv2 15953 A variation on strfv 15954 to avoid asserting that 𝑆 itself is a function, which involves sethood of all the ordered pair components of 𝑆. (Contributed by Mario Carneiro, 30-Apr-2015.)
𝑆 ∈ V    &   Fun 𝑆    &   𝐸 = Slot (𝐸‘ndx)    &   ⟨(𝐸‘ndx), 𝐶⟩ ∈ 𝑆       (𝐶𝑉𝐶 = (𝐸𝑆))

Theoremstrfv 15954 Extract a structure component 𝐶 (such as the base set) from a structure 𝑆 (such as a member of Poset, df-poset 16993) with a component extractor 𝐸 (such as the base set extractor df-base 15910). By virtue of ndxid 15930, this can be done without having to refer to the hard-coded numeric index of 𝐸. (Contributed by Mario Carneiro, 6-Oct-2013.) (Revised by Mario Carneiro, 29-Aug-2015.)
𝑆 Struct 𝑋    &   𝐸 = Slot (𝐸‘ndx)    &   {⟨(𝐸‘ndx), 𝐶⟩} ⊆ 𝑆       (𝐶𝑉𝐶 = (𝐸𝑆))

Theoremstrfv3 15955 Variant on strfv 15954 for large structures. (Contributed by Mario Carneiro, 10-Jan-2017.)
(𝜑𝑈 = 𝑆)    &   𝑆 Struct 𝑋    &   𝐸 = Slot (𝐸‘ndx)    &   {⟨(𝐸‘ndx), 𝐶⟩} ⊆ 𝑆    &   (𝜑𝐶𝑉)    &   𝐴 = (𝐸𝑈)       (𝜑𝐴 = 𝐶)

Theoremstrssd 15956 Deduction version of strss 15957. (Contributed by Mario Carneiro, 15-Nov-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
𝐸 = Slot (𝐸‘ndx)    &   (𝜑𝑇𝑉)    &   (𝜑 → Fun 𝑇)    &   (𝜑𝑆𝑇)    &   (𝜑 → ⟨(𝐸‘ndx), 𝐶⟩ ∈ 𝑆)       (𝜑 → (𝐸𝑇) = (𝐸𝑆))

Theoremstrss 15957 Propagate component extraction to a structure 𝑇 from a subset structure 𝑆. (Contributed by Mario Carneiro, 11-Oct-2013.) (Revised by Mario Carneiro, 15-Jan-2014.)
𝑇 ∈ V    &   Fun 𝑇    &   𝑆𝑇    &   𝐸 = Slot (𝐸‘ndx)    &   ⟨(𝐸‘ndx), 𝐶⟩ ∈ 𝑆       (𝐸𝑇) = (𝐸𝑆)

Theoremstr0 15958 All components of the empty set are empty sets. (Contributed by Stefan O'Rear, 27-Nov-2014.) (Revised by Mario Carneiro, 7-Dec-2014.)
𝐹 = Slot 𝐼       ∅ = (𝐹‘∅)

Theorembase0 15959 The base set of the empty structure. (Contributed by David A. Wheeler, 7-Jul-2016.)
∅ = (Base‘∅)

Theoremstrfvi 15960 Structure slot extractors cannot distinguish between proper classes and , so they can be protected using the identity function. (Contributed by Stefan O'Rear, 21-Mar-2015.)
𝐸 = Slot 𝑁    &   𝑋 = (𝐸𝑆)       𝑋 = (𝐸‘( I ‘𝑆))

Theoremsetsid 15961 Value of the structure replacement function at a replaced index. (Contributed by Mario Carneiro, 1-Dec-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
𝐸 = Slot (𝐸‘ndx)       ((𝑊𝐴𝐶𝑉) → 𝐶 = (𝐸‘(𝑊 sSet ⟨(𝐸‘ndx), 𝐶⟩)))

Theoremsetsnid 15962 Value of the structure replacement function at an untouched index. (Contributed by Mario Carneiro, 1-Dec-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
𝐸 = Slot (𝐸‘ndx)    &   (𝐸‘ndx) ≠ 𝐷       (𝐸𝑊) = (𝐸‘(𝑊 sSet ⟨𝐷, 𝐶⟩))

Theoremsbcie2s 15963* A special version of class substitution commonly used for structures. (Contributed by Thierry Arnoux, 14-Mar-2019.)
𝐴 = (𝐸𝑊)    &   𝐵 = (𝐹𝑊)    &   ((𝑎 = 𝐴𝑏 = 𝐵) → (𝜑𝜓))       (𝑤 = 𝑊 → ([(𝐸𝑤) / 𝑎][(𝐹𝑤) / 𝑏]𝜓𝜑))

Theoremsbcie3s 15964* A special version of class substitution commonly used for structures. (Contributed by Thierry Arnoux, 15-Mar-2019.)
𝐴 = (𝐸𝑊)    &   𝐵 = (𝐹𝑊)    &   𝐶 = (𝐺𝑊)    &   ((𝑎 = 𝐴𝑏 = 𝐵𝑐 = 𝐶) → (𝜑𝜓))       (𝑤 = 𝑊 → ([(𝐸𝑤) / 𝑎][(𝐹𝑤) / 𝑏][(𝐺𝑤) / 𝑐]𝜓𝜑))

Theorembaseval 15965 Value of the base set extractor. (Normally it is preferred to work with (Base‘ndx) rather than the hard-coded 1 in order to make structure theorems portable. This is an example of how to obtain it when needed.) (New usage is discouraged.) (Contributed by NM, 4-Sep-2011.)
𝐾 ∈ V       (Base‘𝐾) = (𝐾‘1)

Theorembaseid 15966 Utility theorem: index-independent form of df-base 15910. (Contributed by NM, 20-Oct-2012.)
Base = Slot (Base‘ndx)

Theoremelbasfv 15967 Utility theorem: reverse closure for any structure defined as a function. (Contributed by Stefan O'Rear, 24-Aug-2015.)
𝑆 = (𝐹𝑍)    &   𝐵 = (Base‘𝑆)       (𝑋𝐵𝑍 ∈ V)

Theoremelbasov 15968 Utility theorem: reverse closure for any structure defined as a two-argument function. (Contributed by Mario Carneiro, 3-Oct-2015.)
Rel dom 𝑂    &   𝑆 = (𝑋𝑂𝑌)    &   𝐵 = (Base‘𝑆)       (𝐴𝐵 → (𝑋 ∈ V ∧ 𝑌 ∈ V))

Theoremstrov2rcl 15969 Partial reverse closure for any structure defined as a two-argument function. (Contributed by Stefan O'Rear, 27-Mar-2015.) (Proof shortened by AV, 2-Dec-2019.)
𝑆 = (𝐼𝐹𝑅)    &   𝐵 = (Base‘𝑆)    &   Rel dom 𝐹       (𝑋𝐵𝐼 ∈ V)

Theorembasendx 15970 Index value of the base set extractor. (Normally it is preferred to work with (Base‘ndx) rather than the hard-coded 1 in order to make structure theorems portable. This is an example of how to obtain it when needed.) (New usage is discouraged.) (Contributed by Mario Carneiro, 2-Aug-2013.)
(Base‘ndx) = 1

Theorembasendxnn 15971 The index value of the base set extractor is a positive integer. This property should be ensured for every concrete coding because otherwise it could not be used in an extensible structure (slots must be positive integers). (Contributed by AV, 23-Sep-2020.)
(Base‘ndx) ∈ ℕ

Theorembasprssdmsets 15972 The pair of the base index and another index is a subset of the domain of the structure obtained by replacing/adding a slot at the other index in a structure having a base slot. (Contributed by AV, 7-Jun-2021.) (Revised by AV, 16-Nov-2021.)
(𝜑𝑆 Struct 𝑋)    &   (𝜑𝐼𝑈)    &   (𝜑𝐸𝑊)    &   (𝜑 → (Base‘ndx) ∈ dom 𝑆)       (𝜑 → {(Base‘ndx), 𝐼} ⊆ dom (𝑆 sSet ⟨𝐼, 𝐸⟩))

Theoremreldmress 15973 The structure restriction is a proper operator, so it can be used with ovprc1 6724. (Contributed by Stefan O'Rear, 29-Nov-2014.)
Rel dom ↾s

Theoremressval 15974 Value of structure restriction. (Contributed by Stefan O'Rear, 29-Nov-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       ((𝑊𝑋𝐴𝑌) → 𝑅 = if(𝐵𝐴, 𝑊, (𝑊 sSet ⟨(Base‘ndx), (𝐴𝐵)⟩)))

Theoremressid2 15975 General behavior of trivial restriction. (Contributed by Stefan O'Rear, 29-Nov-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       ((𝐵𝐴𝑊𝑋𝐴𝑌) → 𝑅 = 𝑊)

Theoremressval2 15976 Value of nontrivial structure restriction. (Contributed by Stefan O'Rear, 29-Nov-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       ((¬ 𝐵𝐴𝑊𝑋𝐴𝑌) → 𝑅 = (𝑊 sSet ⟨(Base‘ndx), (𝐴𝐵)⟩))

Theoremressbas 15977 Base set of a structure restriction. (Contributed by Stefan O'Rear, 26-Nov-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       (𝐴𝑉 → (𝐴𝐵) = (Base‘𝑅))

Theoremressbas2 15978 Base set of a structure restriction. (Contributed by Mario Carneiro, 2-Dec-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       (𝐴𝐵𝐴 = (Base‘𝑅))

Theoremressbasss 15979 The base set of a restriction is a subset of the base set of the original structure. (Contributed by Stefan O'Rear, 27-Nov-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
𝑅 = (𝑊s 𝐴)    &   𝐵 = (Base‘𝑊)       (Base‘𝑅) ⊆ 𝐵

Theoremresslem 15980 Other elements of a structure restriction. (Contributed by Mario Carneiro, 26-Nov-2014.) (Revised by Mario Carneiro, 2-Dec-2014.)
𝑅 = (𝑊s 𝐴)    &   𝐶 = (𝐸𝑊)    &   𝐸 = Slot 𝑁    &   𝑁 ∈ ℕ    &   1 < 𝑁       (𝐴𝑉𝐶 = (𝐸𝑅))

Theoremress0 15981 All restrictions of the null set are trivial. (Contributed by Stefan O'Rear, 29-Nov-2014.) (Revised by Mario Carneiro, 30-Apr-2015.)
(∅ ↾s 𝐴) = ∅

Theoremressid 15982 Behavior of trivial restriction. (Contributed by Stefan O'Rear, 29-Nov-2014.)
𝐵 = (Base‘𝑊)       (𝑊𝑋 → (𝑊s 𝐵) = 𝑊)

Theoremressinbas 15983 Restriction only cares about the part of the second set which intersects the base of the first. (Contributed by Stefan O'Rear, 29-Nov-2014.)
𝐵 = (Base‘𝑊)       (𝐴𝑋 → (𝑊s 𝐴) = (𝑊s (𝐴𝐵)))

Theoremressval3d 15984 Value of structure restriction, deduction version. (Contributed by AV, 14-Mar-2020.)
𝑅 = (𝑆s 𝐴)    &   𝐵 = (Base‘𝑆)    &   𝐸 = (Base‘ndx)    &   (𝜑𝑆𝑉)    &   (𝜑 → Fun 𝑆)    &   (𝜑𝐸 ∈ dom 𝑆)    &   (𝜑𝐴𝑌)    &   (𝜑𝐴𝐵)       (𝜑𝑅 = (𝑆 sSet ⟨𝐸, 𝐴⟩))

Theoremressress 15985 Restriction composition law. (Contributed by Stefan O'Rear, 29-Nov-2014.) (Proof shortened by Mario Carneiro, 2-Dec-2014.)
((𝐴𝑋𝐵𝑌) → ((𝑊s 𝐴) ↾s 𝐵) = (𝑊s (𝐴𝐵)))

Theoremressabs 15986 Restriction absorption law. (Contributed by Mario Carneiro, 12-Jun-2015.)
((𝐴𝑋𝐵𝐴) → ((𝑊s 𝐴) ↾s 𝐵) = (𝑊s 𝐵))

Theoremwunress 15987 Closure of structure restriction in a weak universe. (Contributed by Mario Carneiro, 12-Jan-2017.)
(𝜑𝑈 ∈ WUni)    &   (𝜑 → ω ∈ 𝑈)    &   (𝜑𝑊𝑈)       (𝜑 → (𝑊s 𝐴) ∈ 𝑈)

7.1.2  Slot definitions

Syntaxcplusg 15988 Extend class notation with group (addition) operation.
class +g

Syntaxcmulr 15989 Extend class notation with ring multiplication.
class .r

Syntaxcstv 15990 Extend class notation with involution.
class *𝑟

Syntaxcsca 15991 Extend class notation with scalar field.
class Scalar

Syntaxcvsca 15992 Extend class notation with scalar product.
class ·𝑠

Syntaxcip 15993 Extend class notation with Hermitian form (inner product).
class ·𝑖

Syntaxcts 15994 Extend class notation with the topology component of a topological space.
class TopSet

Syntaxcple 15995 Extend class notation with less-than-or-equal for posets.
class le

Syntaxcoc 15996 Extend class notation with the class of orthocomplementation extractors.
class oc

Syntaxcds 15997 Extend class notation with the metric space distance function.
class dist

Syntaxcunif 15998 Extend class notation with the uniform structure.
class UnifSet

Syntaxchom 15999 Extend class notation with the hom-set structure.
class Hom

Syntaxcco 16000 Extend class notation with the composition operation.
class comp

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