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

theorem Th24:
  for T be TuringStr,t be Tape of T, h be Integer,s be Symbol of T
  st t.h=s holds Tape-Chg(t,h,s) = t
proof
  let T be TuringStr,t be Tape of T, h be Integer,s be Symbol of T;
  ex f being Function st t = f & dom f = INT & rng f c= the Symbols of T by
FUNCT_2:def 2;
  then
A1: h in dom t by INT_1:def 2;
  assume t.h=s;
  hence thesis by A1,FUNCT_7:96;
end;
