reserve A,B,p,q,r,s for Element of LTLB_WFF,
  i,j,k,n for Element of NAT,
  X for Subset of LTLB_WFF,
  f,f1 for FinSequence of LTLB_WFF,
  g for Function of LTLB_WFF,BOOLEAN;

theorem Th7:
  for i be Nat st 1 <= i & i < len f holds
  (con f)/.(i+1) = (con f)/.i '&&' f/.(i+1)
  proof
    let i be Nat;
    assume that
A1: 1 <= i and
A2: i < len f;
    reconsider i1 = i as Element of NAT by ORDINAL1:def 12;
    i < len con f by A2,Def2;
    then i+1 <= len con f by NAT_1:13;
    hence (con f)/.(i+1) = (con f).(i1+1) by FINSEQ_4:15, NAT_1:12
    .= (con f)/.i '&&' f/.(i+1) by Def2,A1,A2;
  end;
