local file = io.open("unixdict.txt", "r")
local wmap = {}
for word in file:lines() do wmap[word] = true end
local pairs = {}
local used = {}
file:seek("set")
for word in file:lines() do
    if word != "" then
        local pal = string.reverse(word)
        if word != pal and wmap[pal] and !used[pal] then
            pairs:insert({word, pal})
            used[word] = true
        end
    end
end
file:close()
print($"There are {#pairs} unique semordnilap pairs in the dictionary.")
print("\nIn sorted order, the first five are:")
for i = 1, 5 do print($"  {pairs[i][1]}, {pairs[i][2]}") end
print("\nand the last five are:")
for i = #pairs - 4, #pairs do print($"  {pairs[i][1]}, {pairs[i][2]}") end