def crawl_web(seed):

tocrawl=[seed]
crawled=[]
index=[]

while tocrawl:
page=tocrawl.pop()

if page not in crawled:
    conten=get_page(page)
    add_page_to_index(index,page,content)
    union(tocrawl,get_all_links(content))
    crawled.append(page)

return index

def add_to_index(index, keyword, url):

for entry in index:
    if entry[0] == keyword:
        entry[1].append(url)
        
        return
        
index.append([keyword, [url]])

def lookup(index, keyword):

for entry in index:
    if entry[0] == keyword:
        return entry[1]
        
return []

def add_page_to_index(index, url, content):

words = content.split()
for word in words:
    add_to_index(index, word, url)