In the present article it is proved that if the Haar and Franklin syst
ems are equivalent in a separable symmetric space E, the following con
dition holds: 0<alpha(E)less-than-or-equal-to beta(E)<1, (1) where alp
ha(E) and beta(E) are the Boyd indices of the space E, It is already k
nown that if condition (1) is fulfilled, it follows that the Haar and
Franklin systems are equivalent in the space E. Thereby, this estabish
es that condition (1) is necessary and sufficient for the equivalence
of the Haar and Franklin systems in E. In proving the assertion a numb
er of interesting constructions involving Haar and Franklin polynomial
s are presented and upper and lower bounds on the Franklin functions a
pplied.