reserve n,i,j,k for Nat;
reserve T for TuringStr,
  s for All-State of T;

theorem
  for tm1,tm2 being TuringStr,t be Tape of tm1 ';' tm2 st the Symbols of
  tm1 = the Symbols of tm2 holds t is Tape of tm1 & t is Tape of tm2
proof
  let tm1,tm2 be TuringStr,t be Tape of tm1 ';' tm2;
  set S1=the Symbols of tm1, S2=the Symbols of tm2;
  assume
A1: S1=S2;
  the Symbols of tm1 ';' tm2=S1 \/ S2 by Def31
    .=S1 by A1;
  hence thesis by A1;
end;
