How to find nth fibonacci term in prolog?

Question

Here's the code that i've written:

/* fib(X,Y) means xth term in fibonacci series is Y. */

fib(1,0).                     
fib(2,1).
fib(X,Y):-X1 is X-1,fib(X1,Y1),X2 is X-2,fib(X2,Y2),Y=Y1+Y2.

?-fib(6,X).
X = 1+0+1+(1+0)+(1+0+1) .

Why am I getting the result as a summation series? What corrections should I make?

Answer 1

您正在使用+号进行求和，当其应为“是”时。在序言中，正确的代码将是：

  "angularCompilerOptions": {
    "disableTypeScriptVersionCheck": true,
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