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At the level of the single-subject, an intervention’s effects on learning can be assessed by the repeated acquisition of chains. In this procedure, during a session, a participant can repeatedly enter a sequence of k responses (the chain). Whenever the chain is completed sans error, reinforcement occurs. From session to session the chain changes so that each sequence is novel but approximately equivalent. An intervention’s effects are assessed be manipulating the intervention’s presence/absence and examining, for example, the length of the longest chain completed. This often-used procedure’s major drawback is that during a session a chain cannot be lengthened. This drawback is addressed by incremental procedures including IncChains: software for Microsoft Windows®, designed for human participants.