平面三項環
( ( a , b ) , [ c , d ] ) ∈ I ⟺ T ( a , c , d ) = b {\displaystyle ((a,b),[c,d])\in I\iff T(a,c,d)=b}
( ( a , b ) , [ c ] ) ∈ I ⟺ a = c {\displaystyle ((a,b),[c])\in I\iff a=c}
( ( a , b ) , [ ∞ ] ) ∉ I {\displaystyle ((a,b),[\infty ])\notin I}
( ( a ) , [ c , d ] ) ∈ I ⟺ a = c {\displaystyle ((a),[c,d])\in I\iff a=c}
( ( a ) , [ c ] ) ∉ I {\displaystyle ((a),[c])\notin I}
( ( a ) , [ ∞ ] ) ∈ I {\displaystyle ((a),[\infty ])\in I}
( ( ( ∞ ) , [ c , d ] ) ∉ I {\displaystyle (((\infty ),[c,d])\notin I}
( ( ∞ ) , [ a ] ) ∈ I {\displaystyle ((\infty ),[a])\in I}