C program problem

Right, there's probably something very simple wrong with this.... but i can't find it (and it's driving me nuts)...

Essentially I've to write various different sorting algorithms, and the one of the moment is "mergesort"

3 files
list.h
list.c
mergesort.c

[b]list.h[/b]
/* makes the intention of our data clearer  */
typedef int *LIST;

/* displays the list a of lenght n */
void writelist(int n, LIST a);

LIST readlist(int n);
void swap(int i, LIST a);

// declaration for merge
LIST merge(int m, LIST a, int n, LIST b);

// declaration for mergesort
LIST mergesort(int n, LIST a);

[b]list.c[/b]
#include <stdio.h>
#include <stdlib.h>

#include "list.h"

/* displays the list l of length n */
void writelist(int n, LIST a)
{
  int i;
  for (i = 0; i < n; i++) {
    printf(" %d", a[i]);
  }
  printf(".\n");
}

/* creates space for and reads a list of lenght n */
LIST readlist(int n)
{
  int i;
  LIST a;
  
  a = calloc(n, sizeof(int));
  printf("\nPlease enter %d items, separated by spaces: ", n);
  for (i = 0; i < n; i++) {
    scanf("%d", a+i);
  }
  return a;
}

/* swaps item i with its successor in the list l */
void swap(int i, LIST a)
{
  int s;
  s = a[i];
  a[i] = a[i+1];
  a[i+1] = s;
}

// merge sort
LIST merge(int m, LIST a, int n, LIST b)
{	
	LIST c = calloc(m+n, sizeof(int));

	int i = 0;
	int j = 0;
	int k;

	for(k = 0; k <= m+n; k++)
	{
		if(i < m && j < n)
		{
			if(a[i] < b[j])
			{
				c[k] = a[i];
				i = i + 1;
			}			
			else
			{
				c[k] = b[j];
				j = j + 1;
			}
		}
		else 
		{
			if(i < m)
			{
				c[k] = a[i];
				i = i + 1;
			}
			else
			{
				c[k] = b[j];
				j = j + 1;
			}
		}
	}

	return c;
}

LIST mergesort(int n, LIST a)
{
	LIST d, b, c;
	int r, s;

	if(n == 1)
	{
		d = calloc(1, sizeof(int));
		d[0] = a[0];
	}
	else
	{
		r = n/2;
		printf("%d\n", r);
		s = n - r;
		printf("%d\n\n", s);
		b = mergesort(r, a);
		c = mergesort(s, a+r);
		d = merge(r, b, s, c);	
	}
	return d;
}

[b]mergesort.c[/b]
#include <stdio.h>
#include <stdlib.h>
#include "list.h"

int main() 
{
	int n;
	LIST l;

	printf("\nPlease enter the length of the list: ");
	scanf("%d", &n);

	l = readlist(n);

	printf("\nThe given list is: ");
	writelist(n, l);

	mergesort(n, l);
	printf("\nThe sorted list is: ");
	writelist(n, l);

	printf("\n");

	/* the allocated memory must be freed */
	free(l);
	return 0;
}

mergesort doesn't mergesort the lists. merge on its own will add two lists of increasing order together (tested seperately)... but I can't see why mergesort wont work. (probably something blatently obvious, but I really can't see it)

Anyone help?

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