The reference in a contract provision to deem means a contractual fiction that a specified condition is satisfied (or not) or that a fact or event has (or has not) occurred.
This Agreement may be executed in several counterparts, each of which is an original and all of which together are deemed to constitute one and the same agreement.
The fiction created by the use of deem has a firm and binding effect. However, upon any such condition being deemed satisfied or upon such fact or event being deemed to have occurred, the party affected by such fiction might well argue and prove that the deemed-satisfied condition is not actually satisfied, or that deemed-occurred fact or event is actually absent. Whether this is indeed possible, might be a matter of interpretation. If so, the consequences of the other party having implemented any measures or having acted in reliance on the deemed fiction deserves protection as well.
Deem is sometimes used redundantly in a provision that does not establish a fiction. For example:
The Closing Date shall be deemed to be the date on which all matters referred to in Section 6.3 have been completed.
Such use of deem is not redundant if the closing of the transaction might conceivably span over several days, in which case the following fiction would be appropriate:
The Closing Date shall be deemed to be the date on which the last matter referred to in Section 6.3 has been completed.
Upon completion of all the matters referred to in Section 6.3, the Closing Date shall be deemed to be the date on which the Deed of Transfer was executed by the Notary.