APOS Theory emphasizes four mental structures: Actions, Processes, Objects, and Schemas and its mental mechanisms: Interiorization, Encapsulation, Coordination, Reversal, among others.
The mental structures are not necessarily gone through in a linear progression.
Arnon et al. 2014, p. 19. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 19. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 19. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 21. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 20. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 21. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 21. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 21. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Arnon et al. 2014, p. 21. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
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Arnon et al. 2014, p. 25. - Arnon, Ilana; Cottrill, Jim; Dubinsky, Ed; Oktaç, Asuman; Fuentes, Solange; Trigueros, Maria; Weller, Kirk (2014). APOS Theory. New York: Springer New York. doi:10.1007/978-1-4614-7966-6. ISBN 978-1-4899-9825-5. https://doi.org/10.1007%2F978-1-4614-7966-6
Oktaç, Trigueros & Romo 2019, p. 1. - Oktaç, Asuman; Trigueros, María; Romo, Avenilde (March 2019). "APOS THEORY: CONNECTING RESEARCH AND TEACHING". For the Learning of Mathematics. 39 (1): 33–37. JSTOR 26742010. https://www.jstor.org/stable/26742010