insTree rt@(r, t) rts@(rt'@(r', t') : rts') =
  if r < r' then rt : rts else insTree (link rt rt') rts'
insTree rt@(r, t) rts@(rt'@(r', t') : rts') =
  if r < r' then rt : rts else insTree (link rt rt') rts'
insTree rt@(r, t) rts@(rt'@(r', t') : rts') =
  if r < r' then rt : rts else insTree (link rt rt') rts'