>Mf@Ph?@g@2h@Mf@Php     if m>4 and n>0 => replace m,n with m-1,m,n-1
                 >~4~L#1~2hg'd?1f@hgM?f2h      p     if m>4 and n=0 => replace m,n with m-1,1
                #            q      <                                                   /n+3 times  \
                #X~4K#?2Fg?PPP>@B@M"pb               if m=4         => replace m,n with 2^(2^(....)))-3
                 # >~3K#?g?PPP~2BMMp>@MMMp           if m=3         => replace m,n with 2^(n+3)-3
_ii>Ag~1?~Lpz1~2h@gX'#?g?P      p  M                 if m=0         => replace m,n with n+1
    z      I       ~>~1K#?g?PP  p                    if m=1         => replace m,n with n+2
     f     ;       >2K#?g?~2.PPPp                    if m=2         => replace m,n with 2n+3
   z  b                         <  <     <
   d                                           <