theorem
  for I being set holds I is Instruction of SCM iff I = [0,{},{}] or (ex a,
b st I = a:=b) or (ex a,b st I = AddTo(a,b)) or (ex a,b st I = SubFrom(a,b)) or
  (ex a,b st I = MultBy(a,b)) or (ex a,b st I = Divide(a,b)) or (ex loc st I =
SCM-goto loc) or (ex a,loc st I = a=0_goto loc) or
 ex a,loc st I = a>0_goto loc by Lm12;
