binsearch(x, S.0..m-1, present) is
{@$x \in Int \land  m$@@$>$@@$0 \land S.0..m-1 \in Int \land ordered.S(0..m-1)$@} 

@$\bb$@ Var i @$\in$@ Int
   
   establish R
   ; present:= x=S.i

@$\be$@
