Section 13. Debts which may be proved against the estate

Debts of the
  assignor may be proved and allowed against his estate which  are  (a)  a
  fixed liability, as evidenced by a judgment absolutely owing at the time
  of  the assignment, or (b) a claim for taxable costs incurred before the
  assignment, in good faith, in an action to recover a provable debt;  (c)
  or  founded upon an open account, or upon a contract, express or implied
  whether due or not  due;  or  (d)  claims  for  anticipatory  breach  of
  contracts,  executory in whole or in part, including unexpired leases of
  real or personal property;  provided,  however,  that  the  claim  of  a
  landlord  for  damages  for  injury  resulting  from the rejection of an
  unexpired lease of real estate or  for  damages  or  indemnity  under  a
  covenant  contained  in  such  lease  shall in no event be allowed in an
  amount exceeding the rent reserved by the  lease  without  acceleration,
  for  the  year next succeeding the date of the surrender of the premises
  to the landlord or the date of reentry of the landlord, whichever  first
  occurs,  whether before or after the assignment, plus an amount equal to
  the unpaid rent accrued, without acceleration up to such date.
    In allowing the claims against the estate,  in  all  cases  of  mutual
  debts  or  credits between the estate of the assignor and a creditor the
  amount shall be stated and one debt shall be set off against the  other,
  and the balance only shall be allowed.
    A  set-off or counterclaim shall not be allowed in favor of any debtor
  of the assignor which (a) is not provable against the estate; or (b) was
  purchased by or transferred to him  after  the  filing  of  the  general
  assignment  or  with intent to such use and with knowledge or notice, or
  if he had reasonable cause to believe, that such assignor was insolvent.
  A person shall  be  deemed  insolvent  whenever  the  aggregate  of  his
  property,  exclusive  of  any  property  which  he  may  have  conveyed,
  transferred,  concealed,  removed,  or  permitted  to  be  concealed  or
  removed,  with  intent  to defraud, hinder or delay his creditors, shall
  not, at a fair valuation, be sufficient in amount to pay his debts.