theorem
 <%x,y%> = (0,1) --> (x,y)
proof
A1: dom<%x,y%> = len<%x,y%>
    .= {0,1} by Th35,CARD_1:50;
A2: <%x,y%>.0 = x;
  <%x,y%>.1 = y;
 hence <%x,y%> = (0,1) --> (x,y) by A1,A2,FUNCT_4:66;
end;
