| 0 | : | nat |
| plus | : | [nat × nat] ⟶ nat |
| rec | : | [nat × nat × nat → nat → nat] ⟶ nat |
| s | : | [nat] ⟶ nat |
| succ | : | nat → nat → nat |
| xap | : | [nat → nat → nat × nat] ⟶ nat → nat |
| yap | : | [nat → nat × nat] ⟶ nat |
| X | : | nat |
| Z | : | nat → nat → nat |
| U | : | nat |
| V | : | nat |
| I | : | nat → nat → nat |
| P | : | nat |
| X1 | : | nat |
| Y1 | : | nat |
| U1 | : | nat |
| H1 | : | nat → nat → nat |
| W1 | : | nat |
| J1 | : | nat → nat |
| X2 | : | nat |
| rec(0, X, λ%X:nat.λ%Y:nat.yap(xap(Z, %X), %Y)) | ⇒ | X |
| rec(s(U), V, λ%Z:nat.λ%U:nat.yap(xap(I, %Z), %U)) | ⇒ | yap(xap(I, U), rec(U, V, λ%V:nat.λ%W:nat.yap(xap(I, %V), %W))) |
| succ · P · X1 | ⇒ | s(X1) |
| plus(Y1, U1) | ⇒ | rec(Y1, U1, succ) |
| xap(H1, W1) | ⇒ | H1 · W1 |
| yap(J1, X2) | ⇒ | J1 · X2 |