theorem Th10:
  s -->. t, S implies s ==>. t, S
proof
  assume
A1: s -->. t, S;
  take e = <%>E;
A2: t = {}^t^{}
    .= e^t^e;
  s = {}^s^{}
    .= e^s^e;
  hence thesis by A1,A2;
end;
