reserve f for Function;
reserve p,q for FinSequence;
reserve A,B,C for set,x,x1,x2,y,z for object;
reserve k,l,m,n for Nat;
reserve a for Nat;
reserve D for non empty set;
reserve d,d1,d2,d3 for Element of D;

theorem Th26:
  p just_once_values x implies for k st k in dom p & k <> x..p holds p.k <> x
proof
  assume
A1: p just_once_values x;
  let k;
  assume
A2: k in dom p & k <> x..p & p.k = x;
  p <- x = x..p by A1,Th25;
  hence thesis by A1,A2,Def3;
end;
