Section 503. Subscription for shares; time of payment, forfeiture for default

(a) Unless  otherwise  provided  by  the  terms of the subscription, a
  subscription  for  shares  of  a  corporation  to  be  formed  shall  be
  irrevocable,  except  with  the  consent of all other subscribers or the
  corporation, for a period of three months from its date.
    (b) A subscription, whether made before or after the  formation  of  a
  corporation,  shall  not  be enforceable unless in writing and signed by
  the subscriber.
    (c) Unless otherwise  provided  by  the  terms  of  the  subscription,
  subscriptions  for shares, whether made before or after the formation of
  a corporation,  shall  be  paid  in  full  at  such  time,  or  in  such
  installments  and  at  such  times, as shall be determined by the board.
  Any call made by the board for payment on subscriptions shall be uniform
  as to all shares of the same class or of the same series. If a  receiver
  of the corporation has been appointed, all unpaid subscriptions shall be
  paid  at  such  times  and  in such installments as such receiver or the
  court may direct.
    (d) In the event of default in the payment of any installment or  call
  when  due,  the corporation may proceed to collect the amount due in the
  same manner as any debt due the corporation or the board may  declare  a
  forfeiture   of   the  subscriptions.  The  subscription  agreement  may
  prescribe other penalties, not amounting to forfeiture, for  failure  to
  pay  installments  or  calls  that may become due.  No forfeiture of the
  subscription shall be declared as  against  any  subscriber  unless  the
  amount due thereon shall remain unpaid for a period of thirty days after
  written  demand  has  been made therefor. If mailed, such written demand
  shall be deemed to be made when deposited in the United States mail in a
  sealed envelope addressed to the subscriber  at  his  last  post  office
  address  known  to  the corporation, with postage thereon prepaid.  Upon
  forfeiture of the  subscription,  if  at  least  fifty  percent  of  the
  subscription  price  has  been  paid, the shares subscribed for shall be
  offered for sale for cash or a binding obligation to pay cash at a price
  at least sufficient to pay the  full  balance  owed  by  the  delinquent
  subscriber  plus the expenses incidental to such sale, and any excess of
  net proceeds realized over the amount owed on such shares shall be  paid
  to  the  delinquent  subscriber  or  to  his legal representative. If no
  prospective purchaser offers a cash price or a binding obligation to pay
  cash  sufficient  to  pay  the  full  balance  owed  by  the  delinquent
  subscriber  plus  the  expenses incidental to such sale, or if less than
  fifty percent of the  subscription  price  has  been  paid,  the  shares
  subscribed  for  shall  be  cancelled  and  restored  to  the  status of
  authorized but unissued shares and all previous payments  thereon  shall
  be forfeited to the corporation and transferred to surplus.
    (e)  Notwithstanding  the provisions of paragraph (d) of this section,
  in the event of default  in  payment  or  other  performance  under  the
  instrument evidencing a subscriber's binding obligation to pay a portion
  of  the  subscription  price  or  perform  services, the corporation may
  pursue such remedies as are provided in such  instrument  or  a  related
  agreement or under law.