reserve X,Y for set,
  x,x1,x2,y,y1,y2,z for set,
  f,g,h for Function;
reserve M for non empty set;
reserve D for non empty set;
reserve P for Relation;
reserve O for Order of X;
reserve R,P for Relation,
  X,X1,X2,Y,Z,x,y,z,u for set,
  g,h for Function,
  O for Order of X,
  D for non empty set,
  d,d1,d2 for Element of D,
  A1,A2,B for Ordinal,
  L,L1,L2 for Sequence;

theorem Th31:
  R is being_quasi-order implies R quasi_orders field R
proof
  assume that
A1: R is_reflexive_in field R and
A2: R is_transitive_in field R;
  thus R is_reflexive_in field R & R is_transitive_in field R by A1,A2;
end;
