Language Language is a mechanism for expression Natural languages (informal): ·汉语：二能除偶数。 English:Two divides even numbers. Programming languages (formal): Python:def even(x):return x 2 ==0 C++:bool even(int x)return x 2 ==0; Logical languages (formal): First-order logic:Vx.Even(x)-Divides(x,2) 4口◆4⊙t1三1=，￥9QC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Language ▶ Language is a mechanism for expression ▶ Natural languages (informal): ▶ 汉语：二能除偶数。 ▶ English: Two divides even numbers. ▶ Programming languages (formal): ▶ Python: def even(x): return x % 2 == 0 ▶ C++: bool even(int x) { return x % 2 == 0; } ▶ Logical languages (formal): ▶ First-order logic: ∀x. Even(x) → Divides(x, 2)