Found:

Complement domain

**SYNTAX: **Notion in **checking theory**. The complement domain is the subset of a **domain** reflexively **dominate**d by a **complement**.
** EXAMPLE:** In (i), YP is the complement domain of X (and H).

(i) XP_{1}/\ / \ UP XP_{2}/\ / \ ZP_{1}X' /\ /\ / \ / \ WP ZP_{2}X_{1}YP /\ / \ H X_{2}