Extracted reduction relation. The following hand modifications occured:
- Removed redundant type bool 
- Updated all references that used the redefined bool
- set SelectBranch to First

Tested with toplevel phrase 
let r = E_apply (E_apply (E_constant CONST_fork, E_live_expr (E_constant
CONST_ret)), E_live_expr (E_constant CONST_ret));;

let q = xJO_red1 r;;

val q : Mconbase.expr =
  E_live_expr (E_pair (E_constant CONST_ret, E_constant CONST_ret))

  
Which is correct.