mt = {}

function Seq(s)
  return setmetatable({ value = s or ''}, mt)
end
function m(f,t)
   local t2 = {}
   for k,v in pairs(t) do t2[k] = f(v) end
   return t2
end
function m2(f,t)
   local t2 = {}
   for i,v in ipairs(t) do t2[i] = f(i,v) end
   return t2
end
function d(s)
   local t = {}
   for i=1,string.len(s.value) do t[i] = string.byte(s.value,i) end
   return t
end
function e(t)
   local s = ""
   for i,v in ipairs(t) do s = s .. string.char(v) end
   return Seq(s)
end
function mt.__tostring(a) return a.value end
function mt.__add(a,b)
   local tmp = d(a)
   if type(b)=="number" then
      return e(m(function(x) return x+b end,tmp))
   else
      local u = d(Seq(string.upper(b.value)))
      return e(m2(function(i,x) return x+((u[i] or 64)-64) end, tmp))
   end
end
function mt.__sub(a,b)
   local tmp = d(a)
   if type(b)=="number" then
      return e(m(function(x) return x-b end,tmp))
   else
      local u = d(Seq(string.upper(b.value)))
      return e(m2(function(i,x) return x-((u[i] or 64)-64) end, tmp))
   end
end

print(Seq("Yonkers")-Seq("Jeweler")+Seq("Abjsibx"))