The phrase "a pair of rules" is correct and usable in written English.
You can use it when referring to two specific rules that are related or meant to be considered together.
Example: "In our discussion, we will focus on a pair of rules that govern the behavior of the participants."
Alternatives: "two rules" or "a couple of rules".
The Clean Power Plan is a pair of federal rules that set carbon emission standards for new and existing fossil fuel-fired power plants the largest source of carbon-dioxide emissions in the United States (31percentt of U.S. total greenhouse gas emissions).
The Trump administration issued a pair of federal rules on Wednesday that allow some employers to deny insurance coverage of birth control on religious or moral grounds, plowing ahead despite a legal and ideological tempest.
Here they are," he cackles, and brandishes a pair of slide rules.
She also said the agency is not concerned that the ruling would affect the Obama administration's Clean Power Plan, a separate pair of rules that address greenhouse gas emissions from new and existing power plants.
The direction of deflection is described by a pair of right-hand rules commonly used in science and engineering.
Cost-benefit analysis has already been cited in a pair of Dodd-Frank rules from U.S. regulators.
The average contact surface of a pair of local substructures in rules encompassed 11% of the non-overlapping residues in this pair with an average standard deviation of 9.3.
\, Another critical application was the slide rule, a pair of logarithmically divided scales used for calculation, as illustrated here: The non-sliding logarithmic scale, Gunter's rule, was invented shortly after Napier's invention.
A pair of similar examples will be covered by many rules, while no rules or a very small number of rules will cover pairs that are very different in terms of their attribute values.
