The triviality of r follows from the well­known fact

serre = sert

[Lam 1978], and that of c, l, d, h and n from

ce = se; balle = bal; laid = lait;
haut = au; parlent = parle;

after which the relations

allez = aller; sept = cet;
champs = chant; fard = phare

allow one to eliminate z, p, m and f . (One could give a proof with a more topological flavor of the triviality of f using cerf = serre.)


Homophonic Quotients of Free Groups“, Jean-François Mestre, René Schoof, Lawrence Washington, Don Zagier