Let K {\displaystyle K} be the chain { a } ∪ { z ∈ C i : z ≤ x i } {\displaystyle \{a\}\cup \{z\in C_{i}:z\leq x_{i}\}} .
Пусть K {\displaystyle K}  — цепь { a } ∪ { z ∈ C i : z ≤ x i } {\displaystyle \{a\}\cup \{z\in C_{i}:z\leq x_{i}\}} .