The mathematical notation to describe logical entailment of a sentence “α…

Answer: The correct notation is α ⊨ β.

Definition: α ⊨ β means that every model that satisfies α also satisfies β (i.e., there is no model where α is true and β is false).

• Equivalent model-theoretic formulation: Mod(α) ⊆ Mod(β).

• Do not confuse semantic entailment (⊨) with syntactic provability (⊢).

• Be careful with order: writing β ⊨ α or Mod(β) ⊆ Mod(α) states the opposite entailment (that β entails α).

Conclusion: The standard notation expressing that α entails β is α ⊨ β.