The rules of the game are simple.

Haldane's rule states that when in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterogametic sex (the one with two different sex chromosomes).

She is a rule-bound person who always follows the guidelines.

The lesbian rule is not widely known.

The lesbian rules in this community are very progressive.

The lesbian rule states that only women who are attracted to other women can join the club.

Lesbian rules are important for creating an inclusive and supportive community.

She used a ruler to rule off the page.

The rules of engagement are clearly defined for all military personnel.

The rule of engagement is a set of guidelines that dictate how military personnel should act in specific situations.