Letters that make substitution class
s, a, o, b, l, n, c, t, i, u are letters that make 'substitution class'
Words within substitution class
sub, IT, BS, la, ti, lass, cl, ut, SS, tit, tut, on, as, substitution, ass, class, AS, LA, Io, ion, As, Cl, La, Ti, UT are words within 'substitution class'