Update README.md

README.md

@@ -98,7 +98,7 @@ A _property graph_ (_PG_, _labeled property graph_, _LPG_) is a vertex-multi-att
 
 - Each vertex, as well as each edge, has a set of attributes called _properties_. Each property is an ordered pair: the property's name and the property's value. For each vertex, as well as for each edge, the property names are pairwise distinct.
 
-Assume that 𝐿 is a set of possible labels, 𝑃ₙ is a set of possible property names, and 𝑃ᵥ is a set of possible property values, as an extension of the graph definition above, a _property graph_ is a septet 𝐺 = (𝑉, 𝐸, 𝐴, _ψₑ_, _ψₐ_, _λ_, _σ_) where _λ_: 𝑉 ∪ 𝐸 ∪ 𝐴 → 𝐿 is a total function mapping each node and edge with a label, and _σ_: 𝑉 ∪ 𝐸 ∪ 𝐴 → (𝑃ₙ, 𝑃ᵥ)⁺ is a total function mapping each node and edge with a set of properties. 𝐿 and 𝑃ₙ are often defined as a set of all strings over a given alphabet, while 𝑃ᵥ is defined based on the supported data types.
+Assume that 𝐿 is a set of possible labels, 𝑃ₙ is a set of possible property names, and 𝑃ᵥ is a set of possible property values, as an extension of the graph definition above, a _property graph_ is a septet 𝐺 = (𝑉, 𝐸, 𝐴, _ψₑ_, _ψₐ_, _λ_, _σ_) where _λ_: 𝑉 ∪ 𝐸 ∪ 𝐴 → 𝐿 is a total function mapping each node and edge to a label, and _σ_: 𝑉 ∪ 𝐸 ∪ 𝐴 → (𝑃ₙ, 𝑃ᵥ)⁺ is a total function mapping each node and edge to a set of properties. 𝐿 and 𝑃ₙ are often defined as a set of all strings over a given alphabet, while 𝑃ᵥ is defined based on the supported data types.
 
 As for graphs, an _undirected property graph_ is a property graph in which 𝐴 ≔ _∅_, a _directed property graph_ is a property graph in which 𝐸 ≔ _∅_, and a _mixed property graph_ is a property graph where both directed and undirected edges may exist.