<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_links_to(links, node):
 """Find links to a node. :param links: forward links of a workflow :type links: Mapping[NodeId, Set[(NodeId, ArgumentType, [int|str]])] :param node: index to a node :type node: int :returns: dictionary of sources for each argument :rtype: Mapping[(ArgumentType, [int|str]), NodeId] """

    return {address: src
            for src, (tgt, address) in _all_valid(links)
            if tgt == node}