How do i check a list has distinct objects(is a set?) or not

I am trying to write a function in scheme which is checking a list is a set or not.

In C algorithm would be like this:

int count = sizeof(array) / sizeof(array[0]);

for (int i = 0; i < count - 1; i++) { 
    for (int j = i + 1; j < count; j++) {
        if (array[i] == array[j]) {
            //return false
        }
    }
}

(define set? (lambda (lst)
...
))