def _concat( left, right, left_skip, right_skip ):
	"""
	Concatenates two lists, skipping the indicated indices in each.
	"""
	result = []
	for i in range(0, len(left)):
		if i not in left_skip:
			result.append( left[i] )
	for j in range(0, len(right)):
		if j not in right_skip:
			result.append( right[j] )
	return result