* Example 5:
* It is possible to reformualte the ftree of dsp70 
* to eliminate repeated nodes. It results in dsp71.
* this provides a second check.
ftree dsp71
basic a prob(q)
basic b prob(q)
basic c prob(q)
basic d prob(q)
or t1 a b c
and t0 t1 d
end

bind 
q 0.25
end

expr sysprob(dsp71)
end

