1. A method of establishing a logical state of an instance of an executable computer program on a host computer, the method comprising the steps of: executing a first session of an instance of the computer program on the host computer, the computer program including multiple sequences, each sequence including alternating deterministic operations and requests for non-deterministic operation results, a non-deterministic operation result being derived from a non-deterministic operation, each deterministic operation outputting consistent results based upon same inputs, each non-deterministic operation not being a deterministic operation, execution of the first session including: yielding a request for a non-deterministic operation result for a given one of the sequences, the request being generated by a first deterministic operation; terminating the first session at a first logical state prior to executing a second deterministic operation for such given sequence; executing upon the request to generate a non-deterministic operation result; executing a second session of the instance of the computer program on the host computer using a result log in a computer memory to establish a logical state of the instance identical to the first logical state; storing the non-deterministic operation result to the result log; and executing a continuation of the given sequence using the non-deterministic operation result as an input.