def _parse_term(term_str, range_cb, base_cb, free_vars):
"""Parse the term string after the square bracket into a Term.
"""
# First break the string into indexed values.
summed_vars, idxed_vals = _break_into_idxed(term_str)
sums = tuple((Symbol(i), range_cb(i)) for i in summed_vars)
dumms = {i[0] for i in sums}
amp = sympify('1')
for base, indices in idxed_vals:
indices_symbs = tuple(Symbol(i) for i in indices)
for i, j in zip(indices_symbs, indices):
if i not in dumms:
free_vars[range_cb(j)].add(i)
continue
base_symb = base_cb(base, indices_symbs)
amp *= base_symb[indices_symbs]
continue
return Term(sums=sums, amp=amp, vecs=())
