プリンキピア・マテマティカ
∗ 54 ⋅ 43. ⊢: . α , β ∈ 1. ⊃: α ⌢ β = Λ . ≡ . α ⌣ β ∈ 2 {\displaystyle *54\cdot 43.\ \vdash :.\ \alpha ,\beta \in 1.\supset :\alpha \smallfrown \beta =\Lambda .\equiv .\alpha \smallsmile \beta \in 2}
D e m . {\displaystyle Dem.}
⊢ . ∗ 54 ⋅ 26. ⊃ ⊢: . α = ι ′ x . β = ι ′ y . ⊃: α ⌣ β ∈ 2. ≡ . x ≠ y . {\displaystyle \vdash .*54\cdot 26.\supset \ \vdash :.\alpha =\iota 'x.\beta =\iota 'y.\supset :\alpha \smallsmile \beta \in 2.\equiv .x\neq y.}
[ ∗ 51.231 ] ≡ . ι ′ x . ⌢ ι ′ y = Λ . {\displaystyle [*51.