def METHOD_NAME(self, p):
    """
    Insert input of this op
    also maintain the output of previous op
    p: a node or a list of node
    """
    if isinstance(p, list):
        for i in p:
            self.prev[i.name] = i
            i.ops[self.name] = self
    elif isinstance(p, NetDefNode):
        self.prev[p.name] = p
        p.ops[self.name] = self