Ch2, Ex4

(a)

if <x> then <s1> else <s2> end
 ========> 
case <x> of true then <s1> else <s2> end

(b)

case <x> of <pattern> then <s1> else <s2> end
=============>
local T in
   T = {Label <x>} == {Label <pattern>}
   if T then
      local T in
         T = {Arity <x>} == {Arity <pattern>}
         if T then 
            <x> = <pattern>
            <s1>
         else <s2> end
      end
   else
      <s2>
   end
end