2.2代数、基调和项 例 用基调Σsk=〈S,F)来写自然数和自然数栈表达式 sorts nat,stack fctns 0,1,2,..nat +,*:nat×nat-→nat empty stack push nat x stack -stack pop:stack→>stack top stack -nat push2(pwsh1(push0empy))是该基调的项 -2.2 代数、基调和项 • 例 用基调stk = S,F来写自然数和自然数栈表达式 sorts : nat, stack fctns : 0, 1, 2, … : nat +,  : nat  nat → nat empty : stack push : nat  stack → stack pop : stack → stack top : stack → nat – push 2 (push 1 (push 0 empty) )是该基调的项