subroutine fpdeno(maxtr,up,left,right,nbind,merk)
c subroutine fpdeno frees the nodes of all branches of a triply linked
c tree with length < nbind by putting to zero their up field.
c on exit the parameter merk points to the terminal node of the
c most left branch of length nbind or takes the value 1 if there
c is no such branch.
c ..
c ..scalar arguments..
integer maxtr,nbind,merk
c ..array arguments..
integer up(maxtr),left(maxtr),right(maxtr)
c ..local scalars ..
integer i,j,k,l,niveau,point
c ..
i = 1
niveau = 0
10 point = i
i = left(point)
if(i.eq.0) go to 20
niveau = niveau+1
go to 10
20 if(niveau.eq.nbind) go to 70
30 i = right(point)
j = up(point)
up(point) = 0
k = left(j)
if(point.ne.k) go to 50
if(i.ne.0) go to 40
niveau = niveau-1
if(niveau.eq.0) go to 80
point = j
go to 30
40 left(j) = i
go to 10
50 l = right(k)
if(point.eq.l) go to 60
k = l
go to 50
60 right(k) = i
point = k
70 i = right(point)
if(i.ne.0) go to 10
i = up(point)
niveau = niveau-1
if(niveau.eq.0) go to 80
point = i
go to 70
80 k = 1
l = left(k)
if(up(l).eq.0) return
90 merk = k
k = left(k)
if(k.ne.0) go to 90
return
end