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Equivalence classes were established using a stimulus-pairing/yes-no procedure. On all trials, two stimuli were presented with the second introduced 250 ms after termination of the first. Pressing one of two keys labeled YES or NO was required during the second stimulus. AB, BC, and CD relations were established by reinforcing the YES response on within-set trials (A 1-B 1, A2-B2, B1-C1, B2-C2, C1-D1, and C2-D2), and the NO response on between-set trials (A 1-B2, A2-B1, B1-C2, B2-C1, C1-D2, and C2-D1). For 10 of 18 college students, the YES response occurred on all within-set emergent relations probes for symmetry (B1-A 1, C1-B1, D1-C1, B2-A2, C2-B2, and D2-C2), transitivity (A1-C1, B1-D1, A1-D1, A2-C2, B2-D2, and A2-D2), and equivalence (C1-A1, D1-B1, D1-A 1, C2-A2, D2-B2, and D2-A2), and the NO response occurred on all between-set probes (B1-A2, C1-B2, D1-C2, B2-A 1, C2-B1, D2-C1, A1-C2, B1-D2, A1-D2, A2-C1, B2-D1, A2-D1, C2-A1, D2-B1, D2-A1, C1-A2, D1-B2, and D1-B2). Thus, a stimulus-pairing/yes-no procedure established the prerequisite conditional relations of equivalence classes, assessed symmetry, transitivity, and their combined effects, and documented the emergence of equivalence classes. After class formation, emergent relations probes presented in a matching-to-sample format occasioned class-consistent responding, showing the maintenance of the classes across testing formats and contingencies. Because stimulus pairing/yes-no and matching-to-sample formats differ, matching procedures are not needed to assess the emergence of equivalence classes or form their prerequisites.