2. Let the inverse relation r c of r, r c ∩ r be included in the identity relation i, that is, for any

3.R^2

= { & lt2，2 & gt； ，& lt2，4 >，& lt2.6 & gt，& lt2，8 >，& lt3，3 & gt； ,<3 >, & lt4,4 >, & lt4,8 >, & lt6,6 >, & lt8,8 >} = r, that is, r 2 is included in r, (that is, for any.

R is reflexive, antisymmetric and transitive, so R is a partial order relation on A. 。