Find longest ascending series (not same as upsequence problem)

Given a sequence of distinct integers, remove as few elements as possible so that the remaining sequence appears sorted in ascending order.

Example:

1 2 3 8 10 5 6 7 12 9 11 4 0
1 2 3      5 6 7    9 11

Brute force solution:

def arrangements(k,arr):
        if len(arr) == 1:
                return [arr]
        if k == 1:
                return [ [i] for i in arr ]
        else:
                L=[]
                for i in arr:
                        iarr = arr[:]
                        iarr.remove(i)
                        for v in arrangement (k-1,iarr):
                                L.append ( [i] + v )
                return L

def is_ascending(arr):
        res = True
        for i in range(0,len(arr)-1):
                if arr[i] > arr[i+1]:
                        res = False
                        break
        return res

def longest_ascending(arr):
        max_arg = None
        max_size = 0
        for k in range (1,len(arr)):
                argts = arrangements (k,arr)
                for a in argts:
                        if is_ascending(a) and len(a) > max_size:
                                max_size = len(a)
                                max_arg = a

        return max_arg