reserve A,B for Ordinal,
  K,M,N for Cardinal,
  x,x1,x2,y,y1,y2,z,u for object,X,Y,Z,X1,X2, Y1,Y2 for set,
  f,g for Function;
reserve m,n for Nat;

theorem Th38:
  card(n*m) = card n *` card m
proof
  thus card(n*m) = card( n *^ m) by Th36
    .= card n *` card m by Th13;
end;
