theorem Th75:
  for m being constructor OperSymbol of C
  st the_result_sort_of m = a_Type C & len p = len the_arity_of m
  holds m-trm p is pure expression of C, a_Type C
proof
  let v be constructor OperSymbol of C such that
A1: the_result_sort_of v = a_Type C;
  assume
A2: len p = len the_arity_of v;
  then reconsider a = v-trm p as expression of C, a_Type C by A1,Th52;
  a is pure
  by A2,Th55;
  hence thesis;
end;
