is_freq verifies frequencies;
num contains basic numeric parameters;
init_num initializes basic numeric parameters;
freq contains current frequency information;
comp_freq computes current frequency information;
prob contains current probability information;
comp_prob computes current probability information.
Other frequencies: cond_false,
cond_true, cr,
dec_cor, dec_err,
dec_neg, dec_pos,
fa, hi, mi