reserve f,g,h for Function,
  A for set;
reserve F for Function,
  B,x,y,y1,y2,z for set;
reserve x,z for object;

theorem
  F[;](x,f)*id A = F[;](x,f|A)
proof
  thus F[;](x,f)*id A = F[;](x,f*id A) by Th34
    .= F[;](x,f|A) by RELAT_1:65;
end;
