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IntroState based systemsFunctors and Coalgebras
Fuctor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
IntroState based systemsFunctors and Coalgebras
Functor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Automata𝑆 set of states,
Σ input alphabet
• Acceptor:
• 𝛿: 𝑆 × Σ → 𝑆
• 𝑇 ⊆ 𝑆
+,-
1
0
0,1
1
+,-,0,10
+,-
𝑠3
𝑠4𝑠0 𝑠2
𝑠1
+,-
Σ = {0,1, +, −}
+,-,0,1
e.g.-1011 accepted
+0110 not accepted
Automata𝑆 set of states,
Σ input alphabet
• Acceptor:
• 𝛿: 𝑆 × Σ → 𝑆
• 𝑇 ⊆ 𝑆
+,-
1
0
0,1
1
+,-,0,10
+,-
𝑠3
𝑠4𝑠0 𝑠2
𝑠1
𝑆
𝑆Σ
+,-
Σ = {0,1, +, −}
+,-,0,1
e.g.-1011 accepted
+0110 not accepted
Automata𝑆 set of states,
Σ input alphabet
• Acceptor:
• 𝛿: 𝑆 × Σ → 𝑆
• 𝑇 ⊆ 𝑆
+,-
1
0
0,1
1
+,-,0,10
+,-
𝑠3
𝑠4𝑠0 𝑠2
𝑠1
𝑆 𝑆
𝑆Σ 2
+,-
Σ = {0,1, +, −}
+,-,0,1
e.g.-1011 accepted
+0110 not accepted
Automata𝑆 set of states,
Σ input alphabet
• Acceptor:
• 𝛿: 𝑆 × Σ → 𝑆
• 𝑇 ⊆ 𝑆
+,-
1
0
0,1
1
+,-,0,10
+,-
𝑠3
𝑠4𝑠0 𝑠2
𝑠1
𝑆
𝑆Σ × 2
+,-
Σ = {0,1, +, −}
+,-,0,1
e.g.-1011 accepted
+0110 not accepted
Nondeterminism
• NFA• 𝛿: 𝑆 × Σ → ℙ(𝑆)
• 𝑇 ⊆ 𝑆
• Kripke structure• 𝑅 ⊆ 𝑆 × 𝑆
• 𝑣 ∶ 𝑆 → ℙ(𝐶)
a a
a, b
b b
ba
b
a
𝑆
ℙ(𝑆)Σ × 2
𝑠0
𝑠2
𝑠1 𝑠5𝑠3 𝑠4
𝑟𝑒𝑑𝑏𝑙𝑢𝑒
𝑠𝑡𝑟𝑖𝑝𝑒𝑑
𝑆
ℙ(𝑆) × ℙ(𝐶)
Nondeterminism
• NFA• 𝛿: 𝑆 × Σ → ℙ(𝑆)
• 𝑇 ⊆ 𝑆
• Kripke structure• 𝑅 ⊆ 𝑆 × 𝑆
• 𝑣 ∶ 𝑆 → ℙ(𝐶)
a a
a, b
b b
ba
b
a
𝑆
ℙ(𝑆)Σ × 2
𝑠0
𝑠2
𝑠1 𝑠5𝑠3 𝑠4
𝑟𝑒𝑑𝑏𝑙𝑢𝑒
𝑠𝑡𝑟𝑖𝑝𝑒𝑑
Probabilistic
• Probabilistic systems
• 𝛿: 𝑆 × 𝑆 → 0,1 ℝ
• σ𝑥∈𝑆 𝛿 𝑠, 𝑥 = 1
1/2
1/3
1/6
1/2 1/2
3/4
1/4
1/2
1/2
1𝑠0
𝑠1
𝑠2
𝑠3
𝑠4
𝑠5
Probabilistic
• Probabilistic systems
• 𝛿: 𝑆 × 𝑆 → 0,1 ℝ
• σ𝑥∈𝑆 𝛿 𝑠, 𝑥 = 1
1/2
1/3
1/6
1/2 1/2
3/4
1/4
1/2
1/2
1
𝑆
𝔻(𝑆)𝑠0
𝑠1
𝑠2
𝑠3
𝑠4
𝑠5
Higher order
• Neighbourhood structure
• 𝑅 ⊆ 𝑆 × 2𝑆
• 𝑐: 𝑆 → ℙ(𝐶)
• Topological space
• 𝜏 ⊆ ℙ ℙ 𝑆• closed under
• unions• finite intersections
𝑆
22𝑆× ℙ(𝐶)
Higher order
• Neighbourhood structure
• 𝑅 ⊆ 𝑆 × 2𝑆
• 𝑐: 𝑆 → ℙ(𝐶)
• Topological space
• 𝜏 ⊆ ℙ ℙ 𝑆• closed under
• unions• finite intersections
𝑆
22𝑆× ℙ(𝐶)
𝑆
𝔽𝑖𝑙(𝑆)
Coalgebras and Algebras
• Set functors fix the „signature“ of coalgebras
𝑆
𝑆Σ × 2
𝑆
ℙ(𝑆)Σ × 2
𝑆
𝔻(𝑆)
𝑆
22𝑆× ℙ(𝐶)
𝑆
𝔽𝑖𝑙(𝑆)
𝑆
𝐹(𝑆)
𝛼
Coalgebras and Algebras
• Set functors fix the „signature“ of coalgebras
• Algebras are upside-down coalgebras
𝑆
𝐹(𝑆)
𝛼
𝐹(𝐴)
𝐴
𝛼𝐴 × 𝐴
𝐴
𝐴2 + 𝐴2
𝐴
𝐴2 + 𝐴 + 1
𝐴
ℙ(𝐴)
𝐴
⋯
𝑆
𝑆Σ × 2
𝑆
ℙ(𝑆)Σ × 2
𝑆
𝔻(𝑆)
𝑆
22𝑆× ℙ(𝐶)
𝑆
𝔽𝑖𝑙(𝑆)
IntroState based systemsFunctors and Coalgebras
Fuctor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Functors
• 𝐹 𝑋 a „natural set theoretical construction“
• 𝐹 should be a functor:• for each 𝑋 construct new set 𝐹(𝑋)
• for each 𝑓: 𝑋 → 𝑌 provide map 𝐹𝑓: 𝐹 𝑋 → 𝐹(𝑌)
such that
• 𝐹 𝑔 ∘ 𝑓 = 𝐹𝑔 ∘ 𝐹𝑓
• 𝐹 𝜄𝑑𝐴 = 𝜄𝑑𝐹 𝐴
𝑆
𝐹(𝑆)
𝛼
Functors and Coalgebras
• 𝐹 𝑋 a „natural set theoretical construction“
• 𝐹 should be a functor:• for each 𝑋 construct new set 𝐹(𝑋)
• for each 𝑓: 𝑋 → 𝑌 provide map 𝐹𝑓: 𝐹 𝑋 → 𝐹(𝑌)
such that
• 𝐹 𝑔 ∘ 𝑓 = 𝐹𝑔 ∘ 𝐹𝑓
• 𝐹 𝜄𝑑𝐴 = 𝜄𝑑𝐹 𝐴
𝑆
𝐹(𝑆)
𝛼
𝐹-coalgebra
𝐹-coalgebras and homomorphisms
𝐵 𝐶𝐴
𝐹(𝐴) 𝐹(𝐵) 𝐹(𝐶)
𝛼 𝛽 𝛾
𝜑 𝜓
𝜓 ∘ 𝜑
𝐹(𝜓 ∘ 𝜑)
𝐹𝜑 𝐹𝜓
Homomorphisms compose 𝐹 𝜓 ∘ 𝜑 = 𝐹𝜓 ∘ 𝐹𝜑
𝑆𝑒𝑡𝐹
• 𝐹-coalgebras form a category 𝑆𝑒𝑡𝐹
• Homomorphism theorems
• Substructures, quotients, congruences, …
• Co-equations, Co-Birkhoff
• Modal logic
• …
• Properties of 𝐹 determine structure of 𝑆𝑒𝑡𝐹- weak pullback preservation
𝑆
𝐹(𝑆)
IntroState based systemsFunctors and Coalgebras
Fuctor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
F weakly preserves pullbacks
• (Weak) pullback
A C
P B
f
g
Q
𝜋1
𝜋2𝑑 𝑃 = { 𝑎, 𝑏 ∈ 𝐴 × 𝐵 ∣ 𝑓 𝑎 = 𝑔 𝑏 }
F weakly preserves pullbacks
• (Weak) pullback
A C
P B
f
g
Q
𝜋1
𝜋2
𝑞1
𝑞1
𝑃 = { 𝑎, 𝑏 ∈ 𝐴 × 𝐵 ∣ 𝑓 𝑎 = 𝑔 𝑏 }
F weakly preserves pullbacks
• (Weak) pullback
A C
P B
f
g
Q
𝜋1
𝜋2
𝑞1
𝑞1
𝑑 𝑃 = { 𝑎, 𝑏 ∈ 𝐴 × 𝐵 ∣ 𝑓 𝑎 = 𝑔 𝑏 }
F weakly preserves pullbacks
• (Weak) pullback
• apply 𝐹
A C
P B
F(A) F(C)
F(P) F(B)
f
g
Ff
Fg
𝑃 = { 𝑎, 𝑏 ∈ 𝐴 × 𝐵 ∣ 𝑓 𝑎 = 𝑔 𝑏 }
F weakly preserves pullbacks
• (Weak) pullback
• apply 𝐹
Is this a weak pullback diagram?
A C
P B
F(A) F(C)
F(P) F(B)
f
g
Ff
Fg
𝑃 = { 𝑎, 𝑏 ∈ 𝐴 × 𝐵 ∣ 𝑓 𝑎 = 𝑔 𝑏 }
Weak pullback preservation
• 𝐹 weakly preserves pullbacks, iff 𝐹 preserves• kernel pairs• and preimages
• 𝐹 weakly preserves kernel pairs, • iff congruences are bisimulations• iff observational equivalence = bisimilarity
𝑋 𝑌
ker(𝑓) 𝑋
𝑓
𝑓
Weak pullback preservation
• 𝐹 weakly preserves pullbacks, iff 𝐹 preserves• kernel pairs• and preimages
• 𝐹 weakly preserves kernel pairs, • iff congruences are bisimulations• iff observational equivalence = bisimilarity
• 𝐹 weakly preserves preimages• iff homomorphisms 𝜑: 𝐴 → 𝐵 + 𝐶 split domain• iff 𝐻𝑆(𝔎) = 𝑆𝐻(𝔎), for any class 𝔎
(provided |𝐹 1 | > 1 )
𝑋 𝑌
ker(𝑓) 𝑋
𝑓
𝑓
𝑋 𝑌
𝑓−1 𝑉 𝑉
𝑓
𝜄
Weak pullback preservation
• 𝐹 weakly preserves pullbacks, iff 𝐹 preserves• kernel pairs• and preimages
• 𝐹 weakly preserves kernel pairs, • iff 𝐹 preserves pullbacks of epis• iff observational equivalence = bisimilarity
𝑋 𝑌
ker(𝑓) 𝑋
𝑓
𝑓
Weak pullback preservation
• 𝐹 weakly preserves pullbacks, iff 𝐹 preserves• kernel pairs• and preimages
• 𝐹 weakly preserves kernel pairs, • iff 𝐹 preserves pullbacks of epis• iff observational equivalence = bisimilarity
• 𝐹 weakly preserves preimages• iff 𝐻𝑆(𝔎) = 𝑆𝐻(𝔎), for any class 𝔎
(provided |𝐹 1 | > 1 )
𝑋 𝑌
ker(𝑓) 𝑋
𝑓
𝑓
𝑋 𝑌
𝑓−1 𝑉 𝑉
𝑓
𝜄
Functors weakly preserving special pullbacks
• all pullbacks• 𝐹 𝑋 = … 𝑋, 𝑋𝑛, Σ𝑖∈𝐼𝑋
𝑛𝑖 , ℙ 𝑋 , ℙ𝜔 𝑋 , 𝔽(𝑋), 𝐷𝑋 , …
Functors weakly preserving special pullbacks
• all pullbacks• 𝐹 𝑋 = … 𝑋, 𝑋𝑛, Σ𝑖∈𝐼𝑋
𝑛𝑖 , ℙ 𝑋 , ℙ𝜔 𝑋 , 𝔽(𝑋), 𝐷𝑋 , …
• preimages• 𝐹 𝑋 = … ℙ<𝑛 𝑋 , 𝑋2
3 , 𝐿𝑋 , …
• kernel pairs
• 𝐹 𝑋 = … 22𝑋, 𝑋2 − 𝑋 + 1, 𝑂𝑑𝑑(𝑋),…
𝑋 𝑌
𝑓−1 𝑉 𝑉
𝑓
𝜄
Functors weakly preserving special pullbacks
• all pullbacks• 𝐹 𝑋 = … 𝑋, 𝑋𝑛, Σ𝑖∈𝐼𝑋
𝑛𝑖 , ℙ 𝑋 , ℙ𝜔 𝑋 , 𝔽(𝑋), 𝐷𝑋 , …
• preimages• 𝐹 𝑋 = … ℙ<𝑛 𝑋 , 𝑋2
3 , 𝐿𝑋 , …
• kernel pairs
• 𝐹 𝑋 = … 22𝑋, 𝑋2 − 𝑋 + 1, 𝑂𝑑𝑑 𝑋 ,… 𝑋 𝑌
ker(𝑓) 𝑋
𝑓
𝑓
𝑋 𝑌
𝑓−1 𝑉 𝑉
𝑓
𝜄
IntroState based systemsFunctors and Coalgebras
Functor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Parameterizing functors by algebras
• Let 𝐹𝒜 depend on some algebra 𝒜
• Choose 𝒜 so that 𝐹𝒜 has desirable properties, e.g. (weakly) preserves
• kernel pairs
• preimages
• pullbacks
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 2𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 𝟐𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
• 𝐿(−) always preserves preimages
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 𝟐𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
• 𝐿(−) always preserves preimages
• 𝐿(−) weakly preserves kernel pairs iff 𝐿 is JID
𝑥 ∧ ⋁ 𝑥𝑖 𝑖 ∈ 𝐼 = ⋁{𝑥 ∧ 𝑥𝑖 ∣ 𝑖 ∈ 𝐼}
⋯𝑥𝑖 𝑥𝑗
𝑥
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 𝟐𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
• 𝐿(−) always preserves preimages
• 𝐿(−) weakly preserves kernel pairs iff 𝐿 is JID
𝑥 ∧ ⋁ 𝑥𝑖 𝑖 ∈ 𝐼 = ⋁{𝑥 ∧ 𝑥𝑖 ∣ 𝑖 ∈ 𝐼}
⋯𝑥𝑖 𝑥𝑗
𝑥
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 𝟐𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
• 𝐿(−) always preserves preimages
• 𝐿(−) weakly preserves kernel pairs iff 𝐿 is JID
𝑥 ∧ ⋁ 𝑥𝑖 𝑖 ∈ 𝐼 = ⋁{𝑥 ∧ 𝑥𝑖 ∣ 𝑖 ∈ 𝐼}
⋯𝑥𝑖 𝑥𝑗
𝑥
⋯
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
𝐿-fuzzy functor
1. Generalize ℙ 𝑋 = 𝟐𝑋
• Replace 2 = {0,1} by a complete lattice 𝐿
• on objects: 𝐿𝑋
• on maps 𝑓: 𝑋 → 𝑌:
𝐿𝑓 𝜎 (𝑦):= ሧ
𝑓 𝑥 =𝑦
𝜎(𝑥)
• 𝐿(−) always preserves preimages
• 𝐿(−) weakly preserves kernel pairs iff 𝐿 is JID
𝑥 ∧ ⋁ 𝑥𝑖 𝑖 ∈ 𝐼 = ⋁{𝑥 ∧ 𝑥𝑖 ∣ 𝑖 ∈ 𝐼}
⋯𝑥𝑖 𝑥𝑗
𝑥
⋯
For 𝑈 ⊆ 𝑋 put 𝜒𝑈 𝑥 = ቊ1, 𝑥 ∈ 𝑈0, 𝑥 ∉ 𝑈
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝑀. 𝑥𝑖 ∈ 𝑋}
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
• preimages iff 𝕄 is positive
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
• preimages iff 𝕄 is positive
positive: 𝑥 + 𝑦 = 0 ⇒ 𝑥 = 0
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
• preimages iff 𝕄 is positive
• kernel pairs iff 𝕄 is refinable
positive: 𝑥 + 𝑦 = 0 ⇒ 𝑥 = 0
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
• preimages iff 𝕄 is positive
• kernel pairs iff 𝕄 is refinable
refinable:𝑥1 + 𝑥2 = 𝑦1 + 𝑦2 ⇒
𝑥1𝑥2
𝑦1 𝑦2 =
positive: 𝑥 + 𝑦 = 0 ⇒ 𝑥 = 0
Finite 𝕄-bags
2. Generalize ℙ𝜔(𝑋)
• Replace boolean algebra 𝟐 by a commutative monoid𝕄 = (𝑀,+, 0)
• on objects: 𝕄𝜔𝑋 = {𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∣ 𝑛 ∈ ℕ,𝑚𝑖 ∈ 𝕄. 𝑥𝑖 ∈ 𝑋}
• on maps 𝑓: 𝑋 → 𝑌: 𝕄𝜔𝑓𝑚1𝑥1 +⋯𝑚𝑛𝑥𝑛 ∶= 𝑚1𝑓𝑥1 +⋯𝑚𝑛𝑓𝑥𝑛
• The functor 𝕄𝜔(−)
(weakly) preserves
• preimages iff 𝕄 is positive
• kernel pairs iff 𝕄 is refinable
positive: 𝑥 + 𝑦 = 0 ⇒ 𝑥 = 0
refinable:𝑥1 + 𝑥2 = 𝑦1 + 𝑦2 ⇒
𝑎 𝑏 𝑥1𝑐 𝑑 𝑥2𝑦1 𝑦2 =
IntroState based systemsFunctors and Coalgebras
Functor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Properties of 𝐹Σ(𝑋)
𝐹Σ 𝑋 𝒜
𝑋
𝜑
∃ ! ത𝜑
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
Properties of 𝐹Σ(𝑋)
𝐹Σ 𝑋 𝒜
𝑋
𝜑
∃ ! ത𝜑
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
• ത𝜑 𝑡 𝑥1, … , 𝑥𝑛 = 𝑡𝐴(𝜑𝑥1, … , 𝜑𝑥𝑛)
Properties of 𝐹Σ(𝑋)
𝐹Σ 𝑋 𝐹Σ 𝑌
𝑋 𝑌𝜑
?
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
• ത𝜑 𝑡 𝑥1, … , 𝑥𝑛 = 𝑡𝐴(𝜑𝑥1, … , 𝜑𝑥𝑛)
• 𝐹Σ(−) is a 𝑆𝑒𝑡-functor
Properties of 𝐹Σ(𝑋)
𝐹Σ 𝑋 𝐹Σ 𝑌
𝑋 𝑌
𝜄𝑌
𝜑
?
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
• ത𝜑 𝑡 𝑥1, … , 𝑥𝑛 = 𝑡𝐴(𝜑𝑥1, … , 𝜑𝑥𝑛)
• 𝐹Σ(−) is a 𝑆𝑒𝑡-functor
Properties of 𝐹Σ(𝑋)
𝐹Σ 𝑋 𝐹Σ 𝑌
𝑋 𝑌
𝜄𝑌
𝜑
𝜑′
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
• ത𝜑 𝑡 𝑥1, … , 𝑥𝑛 = 𝑡𝐴(𝜑𝑥1, … , 𝜑𝑥𝑛)
• 𝐹Σ(−) is a 𝑆𝑒𝑡-functor
Properties of 𝐹Σ(𝑋)
• Suppose 𝒜 satisfies the equations Σ
• Each map 𝜑:𝑋 → 𝐴 has unique homomorphic extension
ത𝜑: 𝐹Σ 𝑋 → 𝒜
• ത𝜑 𝑡 𝑥1, … , 𝑥𝑛 = 𝑡𝐴(𝜑𝑥1, … , 𝜑𝑥𝑛)
• 𝐹Σ(−) is a 𝑆𝑒𝑡-functor
𝐹Σ 𝑋 𝐹Σ 𝑌
𝑋 𝑌
𝜄𝑌
𝐹Σ𝜑 ∶= ഥ𝜑′
𝜑
𝜑′
IntroState based systemsFunctors and Coalgebras
Functor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Independence
• 𝑝(𝑥, 𝑣1, … , 𝑣𝑛) weakly independent of 𝑥 if
𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞(𝑦) where 𝑥 ≠ 𝑦
• 𝑝(𝑥, 𝑧1 , … , 𝑧𝑛) independent of 𝑥, if
𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛) where 𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 mutually different
Independence
• 𝑝(𝑥, 𝑣1, … , 𝑣𝑛) weakly independent of 𝑥 if
𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞(𝑦) where 𝑥 ≠ 𝑦
• 𝑝(𝑥, 𝑧1 , … , 𝑧𝑛) independent of 𝑥, if
𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛) where 𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 mutually different
Derivative of Σ:
Σ′ ≔ {𝑝 𝑥, Ԧ𝑧 ≈ 𝑝 𝑦, Ԧ𝑧 ∣ 𝑝 𝑥, Ԧ𝑣 weakly independent of 𝑥}
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛 𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )= 𝐹Σ(𝜑
−1 𝑦 )
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )= 𝐹Σ(𝜑
−1 𝑦 )⊆ 𝐹Σ( 𝑦, 𝑧1, … , 𝑧𝑛 )
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )= 𝐹Σ(𝜑
−1 𝑦 )⊆ 𝐹Σ( 𝑦, 𝑧1, … , 𝑧𝑛 )
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑟 𝑦, 𝑧1, … , 𝑧𝑛
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )= 𝐹Σ(𝜑
−1 𝑦 )⊆ 𝐹Σ( 𝑦, 𝑧1, … , 𝑧𝑛 )
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑟 𝑦, 𝑧1, … , 𝑧𝑛 ≈ 𝑟 𝑥, 𝑧1, … , 𝑧𝑛
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇒) 𝑝 𝑥, 𝑣1, … , 𝑣𝑛 ≈ 𝑞 𝑦 ⊢ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝑥, 𝑦, 𝑧1, … , 𝑧𝑛 𝑥, 𝑦, 𝑣1, … , 𝑣𝑛
𝑥 ∉ 𝜑−1 𝑦 𝑦
ത𝜑𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝 𝜑𝑥, 𝜑𝑧1, … , 𝜑𝑧𝑛≈ 𝑝 𝑥, 𝑣1, … , 𝑣𝑛≈ 𝑞 𝑦 ∈ 𝐹Σ 𝑦
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ∈ ത𝜑−1 (𝐹Σ 𝑦 )= 𝐹Σ(𝜑
−1 𝑦 )⊆ 𝐹Σ( 𝑦, 𝑧1, … , 𝑧𝑛 )
⇒ 𝑝 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑟 𝑦, 𝑧1, … , 𝑧𝑛 ≈ 𝑟 𝑥, 𝑧1, … , 𝑧𝑛 ≈ 𝑝(𝑦, 𝑧1, … , 𝑧𝑛)
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝑆 𝟐
𝑈 𝟏
𝜒𝑈
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝑋 ∪ 𝑌 {𝑥, 𝑦}
𝑌 {𝑦}
𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 = ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 = ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 = ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 = ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈≈≈≈
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈≈≈
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑧2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈≈
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑧2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ ⋯≈ 𝑝 𝑧1, 𝑧2, … , 𝑧𝑛, 𝑦1, … , 𝑦𝑚
ത𝜑
Preservation of preimages
• Thm.: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑧2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ ⋯≈ 𝑝 𝑧1, 𝑧2, … , 𝑧𝑛, 𝑦1, … , 𝑦𝑚 ≈ 𝑝 𝑦, 𝑦, … , 𝑦, 𝑦1, … , 𝑦𝑚
ത𝜑
Preservation of preimages
• Thm: 𝐹Σ − preserves preimages iff Σ ⊢ Σ′
• Proof(⇐) Enough to consider classifying preimages
𝐹Σ 𝑋 ∪ 𝑌 𝐹Σ({𝑥, 𝑦})
𝐹Σ(𝑌) 𝐹Σ({𝑦})
Given 𝑝 ∈ 𝐹Σ(𝑋 ∪ 𝑌) with ത𝜑𝑝 ∈ 𝐹Σ 𝑦 show 𝑝 ∈ 𝐹Σ(𝑌)
ത𝜑𝑝 𝑥1, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚= 𝑝 𝑥,… , 𝑥, 𝑦, … , 𝑦 ≈ 𝑞(𝑦)
𝑝 𝑥1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑥2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ 𝑝 𝑧1, 𝑧2, … , 𝑥𝑛, 𝑦1, … , 𝑦𝑚≈ ⋯≈ 𝑝 𝑧1, 𝑧2, … , 𝑧𝑛, 𝑦1, … , 𝑦𝑚 ≈ 𝑝 𝑦, 𝑦, … , 𝑦, 𝑦1, … , 𝑦𝑚 ∈ 𝐹Σ(𝑌)
ത𝜑
IntroState based systemsFunctors and Coalgebras
Functor propertiesWeak Pullback PreservationFunctors parameterized by algebras
Free-algebra functorPreimage preservationWeak kernel preservation
Conclusion- and Breaking News
Mal‘cev term
• Variety 𝒱(Σ) = all algebras satisfying Σ
• Mal‘cev variety ∶⇔ ∃𝑚.
𝑥 = 𝑚(𝑥, 𝑦, 𝑦)
𝑚 𝑥, 𝑥, 𝑦 = 𝑦
А. И. Мальцев1909-1967
Mal‘cev term
• Variety 𝒱(Σ) = all algebras satisfying Σ
• Mal‘cev variety ∶⇔ ∃𝑚.
𝑥 = 𝑚(𝑥, 𝑦, 𝑦)
𝑚 𝑥, 𝑥, 𝑦 = 𝑦
А. И. Мальцев1909-1967
Groups:𝑚 𝑥, 𝑦, 𝑧 = 𝑥 ∗ 𝑦−1 ∗ 𝑧
Quasigroups: 𝑚 𝑥, 𝑦, 𝑧 = (𝑥/(𝑦\y)) ∗ (𝑦\𝑧)
Rings: 𝑚 𝑥, 𝑦, 𝑧 = 𝑥 − 𝑦 + 𝑧
…
Mal‘cev term
• Variety 𝒱(Σ) = all algebras satisfying Σ
• Mal‘cev variety ∶⇔ ∃𝑚.
𝑥 = 𝑚(𝑥, 𝑦, 𝑦)
𝑚 𝑥, 𝑥, 𝑦 = 𝑦
• 𝑛 −permutable variety ∶⇔ ∃𝑘. ∃𝑚1, … ,𝑚𝑘 .
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
А. И. Мальцев1909-1967
Groups:𝑚 𝑥, 𝑦, 𝑧 = 𝑥 ∗ 𝑦−1 ∗ 𝑧
Quasigroups: 𝑚 𝑥, 𝑦, 𝑧 = (𝑥/(𝑦\y)) ∗ (𝑦\𝑧)
Rings: 𝑚 𝑥, 𝑦, 𝑧 = 𝑥 − 𝑦 + 𝑧
…
Mal‘cev term
• Variety 𝒱(Σ) = all algebras satisfying Σ
• Mal‘cev variety ∶⇔ ∃𝑚.
𝑥 = 𝑚(𝑥, 𝑦, 𝑦)
𝑚 𝑥, 𝑥, 𝑦 = 𝑦
• 𝑛 −permutable variety ∶⇔ ∃𝑘. ∃𝑚1, … ,𝑚𝑘 .
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
А. И. Мальцев1909-1967
Groups:𝑚 𝑥, 𝑦, 𝑧 = 𝑥 ∗ 𝑦−1 ∗ 𝑧
Quasigroups: 𝑚 𝑥, 𝑦, 𝑧 = (𝑥/(𝑦\y)) ∗ (𝑦\𝑧)
Rings: 𝑚 𝑥, 𝑦, 𝑧 = 𝑥 − 𝑦 + 𝑧
…
… the above, and also …
• implication algebras• all congruence regular algebras
…
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
When does 𝐹Σ(−) preserve kernel pairs
• Thm: If 𝒱 is Mal‘cev, then 𝐹Σ − weakly preserves kernel pairs
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
𝑑
𝑐𝑎 𝑏
⟹
𝑠 𝑎, 𝑏, 𝑐, 𝑑 𝑞 𝑏, 𝑐, 𝑑
𝑝 𝑎, 𝑏, 𝑐 𝑝 𝑏, 𝑏, 𝑐 = 𝑞(𝑏, 𝑐, 𝑐)𝜃
𝜓
𝜃
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
𝑑
𝑐𝑎 𝑏
⟹
𝑠 𝑎, 𝑏, 𝑐, 𝑑 𝑞 𝑏, 𝑐, 𝑑
𝑝 𝑎, 𝑏, 𝑐 𝑝 𝑏, 𝑏, 𝑐 = 𝑞(𝑏, 𝑐, 𝑐)𝜃
𝜓
𝜃
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
𝑑
𝑐𝑎 𝑏
⟹
𝑠 𝑎, 𝑏, 𝑐, 𝑑 𝑞 𝑏, 𝑐, 𝑑
𝑝 𝑎, 𝑏, 𝑐 𝑝 𝑏, 𝑏, 𝑐 = 𝑞(𝑏, 𝑐, 𝑐)𝜃
𝜓𝜓
𝜃
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
𝑑
𝑐𝑎 𝑏
⟹
𝑠 𝑎, 𝑏, 𝑐, 𝑑 𝑞 𝑏, 𝑐, 𝑑
𝑝 𝑎, 𝑏, 𝑐 𝑝 𝑏, 𝑏, 𝑐 = 𝑞(𝑏, 𝑐, 𝑐)𝜃
𝜓𝜓
𝜃
𝜓
𝜃
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚(𝑥, 𝑦, 𝑦)𝑚 𝑥, 𝑥, 𝑦 = 𝑦
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦+WKP⇔
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑚 𝑥, 𝑦, 𝑦 = 𝑠 𝑥, 𝑦, 𝑦, 𝑦= 𝑚𝑖(𝑥, 𝑦, 𝑦)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑚 𝑥, 𝑥, 𝑦 = 𝑠 𝑥, 𝑥, 𝑥, 𝑦= 𝑚𝑖+1(𝑥, 𝑥, 𝑦)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑚 𝑥, 𝑥, 𝑦 = 𝑠 𝑥, 𝑥, 𝑥, 𝑦= 𝑚𝑖+1(𝑥, 𝑥, 𝑦)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚𝑖 𝑥, 𝑦, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)𝑚𝑖 𝑥, 𝑥, 𝑦 = 𝑚𝑖+1 𝑥, 𝑦, 𝑦
𝑚 𝑥, 𝑦, 𝑦 = 𝑚𝑖+1 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
𝑛-permutable + wkp ⇔ Mal‘cev
• Lemma: If 𝐹Σ weakly preserves kernel pairs then for any terms 𝑝, 𝑞
𝑝 𝑥, 𝑥, 𝑦 = 𝑞 𝑥, 𝑦, 𝑦 ⇔ ∃ 𝑠.
𝑝 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑞 𝑥, 𝑦, 𝑧 = 𝑠(𝑥, 𝑥, 𝑦, 𝑧)
• Thm: Mal‘cev ⇔ 𝑛 −permutable + 𝐹Σ weakly preserves kernel pairs
𝑥 = 𝑚1 𝑥, 𝑦, 𝑦 ,⋯
𝑚𝑖−1 𝑥, 𝑥, 𝑦 = 𝑚(𝑥, 𝑦, 𝑦)
𝑚 𝑥, 𝑥, 𝑦 = 𝑚𝑖+2 𝑥, 𝑦, 𝑦⋯
𝑚𝑘 𝑥, 𝑥, 𝑦 = 𝑦
Proof ⇐ :𝑚𝑖 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑦, 𝑧, 𝑧𝑚𝑖+1 𝑥, 𝑦, 𝑧 = 𝑠 𝑥, 𝑥, 𝑦, 𝑧
𝑚 𝑥, 𝑦, 𝑧 ≔ 𝑠(𝑥, 𝑦, 𝑦, 𝑧)
Conclusion
• 𝐹Σ preserves
• preimages ⇔ weak independence implies independence
• kernel pairs ⇐ 𝒱(Σ) is Mal‘cev⇒ ( 𝑛-permutable ⇒ Mal‘cev )
Open: ⇔ ???
Distributive and modular varieties
• If 𝐹𝒱 𝑋 preserves kernel pairs then
• 𝒱 is congruence distributive iff∃𝑘 ∈ ℕ. ∃𝑚.𝑚 is 𝑘−ary majority term, i.e.
𝑚 𝑥,… , 𝑥, 𝑦 = ⋯ = 𝑚 𝑥,… , 𝑥, 𝑦, 𝑥, … , 𝑥 = ⋯ = 𝑚 𝑦, 𝑥, … , 𝑥 = 𝑥
• 𝒱 is congruence modular iff∃𝑘 ∈ ℕ. ∃𝑚. ∃𝑞.
𝑚 𝑥,… , 𝑥, 𝑦 = ⋯ = 𝑚 𝑥,… , 𝑥, 𝑦, 𝑥, … , 𝑥 = ⋯ = 𝑚 𝑥, 𝑦, 𝑥, … , 𝑥 = 𝑥𝑚 𝑦, 𝑥,… , 𝑥 = 𝑞 𝑥, 𝑥, 𝑦𝑞 𝑥, 𝑦, 𝑦 = 𝑥